This is a collection of stuff that I found out to be useful while playing Returnal. This guide is aimed for those that don't do so well in the game (like myself). Feel free to add your own tips that are not covered here!
In this guide we'll talk a bit about useful settings, user interface terminology, my preferred weapons that I feel it makes my life easier, items (passives) that are cool and some stuff that the game does not do a great job explaining (or you might've missed it)

For now, this is a work in progress.
All screenshots are taken by me.
IGN links were provided where applicable for full lists.

UI explained


Economy pickables

• Obolites (yellow) - Main economy resource that you can use to buy items. They drop after killing enemies;
  
  
• Obolite chunk - Found around the map and usually give between 13-15 obolites;
  
  
• Malignant obolite chunk (purple with yellow) - Gives 40-50 obolites when destroyed with melee. It has a chance to cause a malfunction to your suit;
  
  
• Silphium (green) - Comes in 3 sizes and heals your HP (integrity) - Low, Moderate and Large. This is transformed in resin if you're full HP;
  
  
• Silphium resin (green) - Fills up one of the 3 HP slots. When all 3 are filled, your max hp will increase (a second bar that will grow with each upgrade);
  
  
• Malignant silphium (dark purple) - healing/health upgrade item that can cause a malfunction;
  
  
• Ether (Bright purple) - Economy item used to clean malignant items, offered to certain machines or to steal dead players equipment without avenging them. Can be found on the map, given as reward for completing the daily challenge or reward for avenging dead players bodies. It does not disappear after death. Can carry up to 30;
  
  
• Other malignant items (dark purple) - Items that when interacted with, usually causes a malfunction on the suit (depending on their chances) and gives restrictions or disadvantages until cleaned; Found on chests or atropian keys;
  
  
• Weapons (red) - Dropped from a miniboss or containers; There is also one before every boss;
  
  
  
• Active consumables (orange) - Found in locked chests, dropped by minibosses or found on the map and can be activated once whenever you need them. They also stack;
  
  
  Other pickable items
  • Weapon calibrators (blue) - Item that can increase your proficiency level (or less than a level);
    
    
  • Atropian keys (blue) - Used to open red doors or chests;
    
    
  • Passive upgrades - Gives an advantage to the player (in stats or abilities);
    
  
  Weapon proficiency explained
  This stat determines the level of the next weapon you will find, as well as it's bonus stats
  
  • Can increase when killing enemies
    
  • Can be max lvl 15 in act 1
    
  • Can be max lvl 30 in act 2
    
  • Can be max lvl 45 in the Tower of Sisyphus
    
  • Guaranteed item when advancing to the next biome
    
  • Resets after each run (level 0 in Act 1 and level 5 in Act 2)
  Adrenaline level explained
  Adrenaline increases when you're killing enemies without getting hit (1 level for 3 kills)
  
  • Level 0 - Nothing
    
  • Level 1 - Enhanced Overload - Increases the reload bar of weapons
    
  • Level 1 - 1 additional projectile that seek enemies
    
  • Level 2 - Enhanced Vision - See traces of enemies through the walls
    
  • Level 2 - 2 additional projectiles that seek enemies
    
  • Level 3 - Enhanced Melee attack - Not sure what exactly upgrades here
    
  • Level 3 - 3 additional projectiles that seek enemies
    
  • Level 4 - 50% more proficiency gain from enemy kills
    
  • Level 4 - 4 additional projectiles that seek enemies
    
  • Level 5 - 50% more obolites from enemies and environment
    
  • Level 5 - 5 additional projectiles that seek enemies
    
  • Level 5 - One extra hit shield before adrenaline is reset
  
  Minimap elements
  
  • Challenge room - Also known as containment room; it has 3 phases, a lot of normal enemies and some mini-bosses; gives a reward at the end and it's required to complete to 100% a biome;
    
    
    
  • Dot or circle inside triangle doors - This means the door is locked, requiring a key to open it
    
  • Dot or circle inside a chest - Same as above but for chests
  
  Environmental lasers, inaccesible places and early navigation
  
  • Red moving lasers - You can dash through this without taking damage;
    
    
  • Bright purple lasers - You cannot dash through this without taking damage, need to use jump, then dash;
    
    
  • Orange energy wall/ barrier - Can be destroyed with melee with the Blade Balancer upgrade (You decide if it's worth spending 250 obolites on this one);
    
    
    
  • Vine walls - Can be destroyed with melee. Usually contains healing or currency;
    
    
  • Locked rooms - Can be opened by attacking a hidden lit button; The button also beeps when using ADS; Usually contains weapon chests or other consumables;
    
    
    
  • Tentacle vines - They will try to eat you if you don't dash; Can be used to reach higher platforms in early game (act 1);
    
  
  Other machines you can interact with - WIP
  
  • Cthonos - Can offer items in exchange for ether; Price increases (4-15); Will give unknown items at first;
    
    
  • Inert Reclaimer - Heals most of your hp and gives 6% max HP;
    
    
  • Reclaimer - Can spawn a random consumable; can damage the player (~60% HP); Does not damage the player if health is red; Doesn't seem to kill the player;
    
    
  • Parasites Extractor - Self explanatory. You go inside and you sacrifice some parasites for a bit of obolites (~57); Can be found in every hub area (before the bosses) or in random rooms;
    
    
  • Datacube processor - This is a machine that you need to bring a special cube item (orange) to be scanned; You will get an item and it will be unlocked to be spawned in the future runs; Can be found in every hub area (before the bosses);
    
    
  • Reconstructor - Can revive you once per biome in exchange of 6 ether; Can also be used by the co-op host;
    
    
  
  Other - WIP
  
  • Chronosis - Co-op initializer; You can host public/private or join others; Can be used once per run (if your joiner leaves or crashes);
    
    
  • Red mass - Mini boss spawning; Locks the doors behind you
    

What to do

• Pick up all the parasites that you find so you can recycle them (you can 100% find one in act 2 before the boss or hub). If you want to feel safer, backtrack and pick them after all the rooms are cleared;
  
  
  
• Try to pick up all the obolites of the dead monsters. Try to kill them one by one so you don't miss any;
  
  
• Use the active consumables(orange), make a habit out of it (I personally forget to use anything besides healing; also die without using them)
  
  
• It is cruel but try to kill all the Chrysoids. They are some harmless gold looking creatures with tentacles that drop (WIP) obolites and sometimes consumables;
  
  
• Interact early with malignant items, especially with the ones giving malfunctions. It's usually easy to complete their requirements for fixing; You can stop doing this later in the game if you're not that sure you can overcome them;
  
  
• Destroy flora (mostly found in biome 3 and under water) Some can drop obolites. Can be destroyed by dashing, melee, walking or shooting it;
  
  
  
  
• Invest time to pick new weapons and research their upgrades. See what kind of weapons fits best for you (more on the weapons chapter below);
  
  
• If you unlocked the grappling hook try to use it often to create distance between you and the enemies, especially when fighting mini-bosses;
  
  
• Try to dodge towards a projectile as it grants invincibility frames. Combine it with jumping; (I usually like to jump first)
  
  
• Try to keep silphium vials for boss fights or you think you might die. Use green consumables around the map as a prio if possible;
  
  
• You can sleep in the bed in Helios to heal back to full HP; the ammount of a small silphium once per run;
  
  
• Try to keep a decent number of Ether on you in case you pick up items that offer you stats based on their number. Or in case you want to use the respawn machine;
  
  
• Don't worry too much about opening weapon chests, there are plenty. Another option generally known in the community is to open them at the end when your weapon proficiency is high for a chance of better weapons;
  
  
• Be on your toes when fighting mini-bosses because some of them can cause malfunction attacks (Red floating orbs) - WIP

What to avoid doing

• Avoid interacting with malignant items before a boss fight because you don't have where to fulfill the requirements and it might make the boss fight harder;
  
  
• Don't go directly to the next biome without exploring everything; it's a good idea especially if you're not that good at the game;
  
  
• Avoid going to containment rooms; they're generally hard and you can easily die
  
  
• Don't stay in one place as it's easy to get cornered by enemies;
  
  
• Don't stay too close to enemies because you will have a less time to react to their attacks;
  
  
• I try to avoid acid pool on enemies death malfunction because I have a habit of walking into them to pick up the obolites. Kinda hard to go around it;
  
  
• HP damage on item pickup malfunction is really not cool. It can mess up with your dreams of maximizing your HP and adrenaline;
  

Stunnable enemies with melee

• Mycomorphs
  
• Tentacle dogs [WIP]

My favourite weapons that also gives me the best results (+ their best modifiers):

• Tachyomatic Carbine - Automatic rifle which has lifesteal if you're lucky
  Leech Rounds - Chance of healing per hit
  Armor Piercing - Projectiles will pierce hostiles and ricochet off surfaces
  High Caliber - Higher damage at the expense of fire rate
  Rising Pitch (best combined with Leech Rounds) - Fires faster the longer the trigger is held
  Hardened - Increases Protection
  
• Hollowseeker - Very high rate of fire, a lot of ammo and a lot of damage with the portals; Gives you a bit of time to dodge while they fire
  Portal Beam/Turret - Creates a projectile-firing portal that targets nearby hostiles
  Waves - Creates a projectile-firing portal that targets nearby hostiles
  
• Thermogenic Launcher
  Full auto - Fires at full-auto mode
  Obolite Magnet - Chances to automatically gather Obolite from killed hostiles
  
• Electropylon Driver - Honorable mention - Fires some persisting lasers that stick to enemies; Good to focus on dodging enemies/bosses attacks rather than actively shooting; Fire a few shots once in a while; Also haven't use it much to see which modifiers are the best.
  
  Other weapons and why I rarely use them
  
  • Spitmaw Blaster - This one is in the middle to be honest. Has really good damage, even rate of fire if you're lucky but it doesn't do that good in long range and it can make you more open to attacks since you have to get closer;
    
  • Dreadbound - Insane damage. Unlimited ammo. The trick is to be close to the enemies because it has a 3 boomerang bullet type meaning that if you use it at long rage you can make a cup of coffee and the bullets will still not return to you in time. High risk good reward type of gun, so I kinda avoid it for this reason;
  
  IGN did a guide HERE if you're interested about what each weapon has to offer

Upgrades that every struggling player should have

• Astronaut Figurine - Can respawn you with ~50% HP after you die
  
  
• Phantom Limb - Eliminating hostiles with a 10% chance to repair integrity
  
  
• Warped Rubber Ball - 5% more repair efficiency per ether carried (caps at 50%)
  
  
• Integrity Augument - 25% to your max HP
  
  
• Two Way Radio - Protection in % per ether carried;
  
• Adrenaline Leech - repairs integrity 2% of damage dealt per adrenaline level, so if my math is correct you can get up to 10% of lifesteal if you're on 5.0;
  
  
• Protection Augument - consider picking this up if you can afford it, especially since some mini bosses and later stages enemies can damage you really really bad (can't remember how many times I got suprised and got instant killed);
  
  
• Integrity Circuit - gains max integrity when fixing and gaining malfunctions - Perfect!
  
  
• Damage Augument - Always nice to have, especially if you feel like your damage is underwhelming;
  

Nice consumables for a dark day

• Silphium vials (heals on use) - Vital for backup for any boss fight or later stages - Guaranteed to be found after fighting the boss and going to the next area
  
• Apex sphere (instant 5.0 adrenaline) - self explanatory, good for that extra damage, seeing through walls and extra obolites
  
• Shield Vial (protection for one hit) - Can be used after your hit from 5.0 adrenaline goes away;

Full list here in THIS guide by IGN.

There are three secrets around the biomes, as far as I know:

• Secret rooms
  
  
  These can contain obolites, chests with weapons, passive/active items, mini-bosses or surprise monster spawns! Enter at your own risk.
  
  
• Hidden rooms in walls
  
  There are some hidden rooms in walls that you can destroy.
  
  
• Glowing eyes statues
  
  
  These drop obolites if destroyed (around 12 obolites). Can also spawn enemies sometimes.
  
  
• Obelisks
  (No image yet)
  
  These can spawn obolites as well, but you can’t see in advance if one has them. – WIP
  
  
• Act 2 – Biome 1 – Echoing Ruins
  
  
  
  
  Area filled with ~200 obolites hidden in the green plants. Cut them with your sword!
  
  - 100% has a lot of obolites hidden in the flora (~200)
  - 100% a shop that sells 1 item
  - 100% at least a consumable or a blue item (upgrade or key)
  - High chance of having lasers guarding the mini shop; if they’re red, don’t worry. Purple ones are deadly (I’ve died 5 times in/out of that place).
  - High chance of 2–3 Strixeras (blue flying tentacle things)
  - Can have 1–3 Chrysoids (golden creatures)
  
  These descriptions + screenshots should help you spot it in your runs.
  
  
• Farming spot – WIP – (@ichigomait)
  
  When teleporting back to T1 or going far enough away, then returning near the spot in the picture, an item will respawn there.
  So far: Obolites and Weapon Proficiency.

Optimised settings - Digital Foundry provided some optimised graphic settings for 2060 Super (Day 0, no patches) for less to none stuttering;
• RT Reflections: OFF
  
• RT Shadows: OFF
  
• Volumetric FOG: High
  
• Ambient Occlusion: Medium
  
• Model Quality: Epic
  
• Particle Quality: High
  
• Shadow Quality: High
  
• Lighting Quality: Epic
  
• Texture Quality: Epic (8GB Vram)
  
• NV: DLSS | Intel: XeSS | AMD: DBS/VRS/FSR
  Video here (17:55):
  

Other settings - WIP

• Enable one click run (instead of keeping the button pressed) - WIP
  
• Make crosshair bigger - WIP
  
• Modify the sensitivity to fit your mouse and style - WIP