Resources are items which drop from all normal missions around the star chart that are used solely for the manufacturing of other items in the Foundry with Blueprints. Other than Orokin Cells, each resource can only be found in specific planet systems. Bundles of resources can also be a reward for alert missions as of Hotfix 9.3.4. Alert resource awards do not come as a set quantity but will yield far more than a normal drop. This is not the case for rare-class resources.
As of Hotfix: The Silver Grove 3, most generic resource disks have been replaced by unique objects that resemble the actual resources themselves. Players can also find resource caches unique to the resource type around the map.

Resources are classified by the method of collection, quantity obtained in each pickup and their primary purposes.

Common Resources
Common resources, like the name implies, can be found very commonly and in quantities of hundreds at a time. They drop from lockers, breakables, normal enemies and bosses.

Uncommon Resources
Uncommon resources, like the name implies, are found uncommonly in quantities usually between 10 and 30. They drop from lockers, breakables, normal enemies and bosses. Some of the uncommon Resources are found in higher quantities between 50 and 100.

Rare Resources
Rare resources will usually drop one at a time. Some drop in higher quantities, like 2 or 3. They are most often found by defeating bosses or a specific type of enemy, and very rarely from common enemies or storage lockers/containers.

Research Resources
Research resources are resources with a distinctive blue color, and are dropped uncommonly from common enemies in quantities of 1 to 3. They are crucial materials for Research.

Navigators
Navigators are orbs that are required to build a variety of keys. Like Research Resources, they can be classified as uncommon or rare depending on different factors such as drop rate or quantity obtained. Currently, Nav Coordinates are dropped uncommonly in storage containers, and Lephantis Nav Coordinates are only found in the Orokin Derelict.

Minerals
Special minerals are acquired through mining in the Plains of Eidolon. They can be refined into gems and are usually used for building equipment purchased in Cetus.

Fish
Fish are acquired through fishing in the Plains of Eidolon. Their organs can be extracted and are usually used for building equipment purchased in Cetus.

For best results, it is recommended to farm resources either solo or in a dedicated group. This will reduce any tensions that might otherwise come up between players who are trying to farm resources and those who have other goals and do not wish to look for resources.

Infestation levels tend to spawn more enemies, which means more chances for resources.
In addition to always being infested, Dark Sector missions all have an increased resource drop rate that varies by individual mission.
The Vacuum sentinel mod picks up materials around you in a good radius, removing the need to focus on manually collecting every last resource drop.
At rank 0, Vacuum still has a respectable 6.5 meter range while costing only two mod capacity. Adding it to every sentinel streamlines resource pickup and should reduce (though not eliminate) the need for dedicated resource farming.
Break everything (except reinforced windows). Look for open containers or crates, and do not be shy to break them open, even if your team decides it's not worth it. Some but not all Area-effect warframe abilities break containers, which can be combined with Vacuum to vastly speed up the process.
If playing a level with a very linear route, explore the entire level, including taking elevators to floors where the objective isn't located to look for more containers. Note, however, that choosing to farm and get left behind may result in a forfeiture of the mission credits, which can only be earned by getting to the extraction point before the timer ends.
Thief's Wit enables the player to spot all breakable crates within range through the mini-map, along with highlighting mods through walls.
Master Thief grants the player a certain chance to open locked lockers (40% at level max).
Scavenge allows a Kubrow to have a 90% chance to open locked lockers. However, this only works on lockers the Kubrow can actually reach and also means giving up Vacuum.
Codex Scanner can be used to see all containers in current room within the range of 50 meters.
Weapons such as the Ignis with large AoE bursts are very useful for breaking multiple containers or Resource formations at once.
Weapons like Orthos Prime or Telos Boltace, with large range and decent attack speed, are also very useful at cracking open containers.
Several Warframe abilities or Augments affect resource drops.
Nekros' Desecrate gives a 54% chance for most enemies killed in a wide radius around him to roll their loot tables again, as well as spawning health orbs that help you keep up the fight, especially against the shield-bypassing Toxic damage used by many Infested enemies. Neither Power Strength nor Power Duration affect this ability; mod for range and efficiency. The Despoil augment is also a good idea, as it makes desecrate entirely self-sustaining and allows you to freely use your energy on other abilities.
The fixed 54% chance makes this the least efficient ability on a per-enemy basis, which is balanced out by its extreme ease of use and lack of augment requirement. This, in combination with Nekros being commonly known as "the farming frame," makes Desecrate a popular choice.
Ivara's Prowl allows her to passively "pickpocket" nearby enemies, releasing one random item from their drop table per enemy. This is slow, only working on one enemy at a time and taking multiple seconds, but prioritizing specific enemies allows for more focused farming efforts and since it leaves affected enemies completely untouched, it can be easily coordinated with other farming abilities used by teammates.
In addition to making the ability itself more efficient, duration mods can reduce pickpocket times significantly. Power Strength mods have no beneficial effect on pickpocket but corrupted mods that reduce power strength give the ability a failure chance, requiring the ability to start over and try again.
Atlas' Ore Gaze augment gives Petrified enemies a base 50% chance to reroll their drop tables. Unlike Desecrate, this is affected by Power Strength(up to a 100% chance at 200% power strength) but is harder to use, only working on enemies that are turned to stone at the time of their deaths. It can be used alongside Desecrate.
"Thawed" enemies are no longer affected by Ore Gaze; increase power duration or coordinate with your teammates to ensure that enemies are killed while still petrified.
Hydroid's Pilfering Swarm doubles the drop chance of all enemies killed while ensnared by Tentacle Swarm and tentacles formed by Hydroid's passive. Drop chance is unaffected by power strength but this is still the most powerful single effect, which is counterbalanced by Tentacle Swarm being difficult to use efficiently in the first place. Its ability to synergize with other farming abilities appears to need more testing.
All ability-affecting mods have their uses with Pilfering Swarm: Despite not affecting the augment or increasing the number of tentacles, power strength scales particularly well with Tentacle Swarm's damage, allowing you to kill enemies and retarget a different horde much more quickly and easily. Likewise, Efficiency allows you to more easily compensate for the difficult targeting and limited number of tentacles. Power Range can be either increased to give the tentacles more room to target groups of enemies or reduced to limit them to smaller choke points. Duration, of course, gives you and your teammates more time to kill ensnared enemies but may be wasteful if you find yourself targeting new groups of enemies often.
A common squad composition for a dedicated farming mission is a Speed Nova - that is, a Nova with less than 100% strength using her Molecular Prime ability, which will speed enemies up instead of slowing them down, a Desecrating Nekros, sometimes with the Despoil augment for ease of use, a Pilfering Swarm Hydroid and an Energy Vampire Trinity to allow the other frames to recast their abilities. A common tactic is to find an easy room and "camp" for a good while, speeding the enemies to the camping location and massacring them.

Alloy Plate - Gabii (Ceres), Draco (Ceres) or Malva (Venus)
Argon Crystal - Any Void Exterminate/Sabotage
Circuits - Draco (Ceres) or Malva (Venus)
Control Module - Any Void Survival/Defence, Hyena Pack (Psamathe, Neptune) or Raptors (Naamah, Europa)

Cryotic - Any Excavation mission
Ferrite - Any Void Survival/Defence, Tikal (Earth) or Apollodorus (Mercury)
Gallium - Assur (Uranus) or Lieutenant Lech Kril ( War, Mars)
Morphics - Wahiba (Mars), Captain Vor (Tolstoj, Mercury) or Apollodorus (Mercury)
Nano Spores - Orokin Derelict Defence/Survival, Akkad (Eris) or Piscinas (Saturn)
Neural Sensors - Cameria (Jupiter), Alad V (Themisto, Jupiter) or Raptors (Naamah, Europa)
Neurodes - Orokin Derelict Assassination/Defence/Survival, Tikal (Earth) or Zabala (Eris)
Orokin Cell - Orokin Derelict Survival, Draco (Ceres) or Piscinas (Saturn)
Oxium - Galatea (Neptune), or Despina (Neptune)
Plastids - Zeugma (Phobos), Ophelia (Uranus) or Zabala (Eris)
Polymer Bundle - Assur (Uranus), Ophelia (Uranus) or Apollodorus (Mercury)
Rubedo - Any Void Survival/Defence or Zeugma (Phobos)
Salvage - Cameria (Jupiter) or Wahiba (Mars)
Tellurium - Ophelia (Uranus), Caelus (Uranus) or Salacia (Neptune)

Alloy Plate - {Venus - Phobes - Ceres - Jupiter - Pluto - Sedna}
Cryotic ------ {Venus - Earth - Phobes - Europa - Neptune}
Ferrite ------- {Mercury - Earth - Lua - Neptune - Void}
Nano Spores - {Saturn - Neptune - Erie - Derelict}
Polymer bundle- {Mercury - Venus - Uranus}
Salvage - {Mars - Jupiter - Sedna}

Circuts - {Venus - Ceres - Kuva Fortress}
Plastids - {Phobos - Saturn - Uranus - Pluto - Erie}
Rubedo - {Earth - Lua - Phobos - Europa - Pluto - Sedna - Void}

Argon - {Void} [Note that collecting them is rare but they disolve while they are outside the void]
Crontol Module - {Europa - Neptune -
Gallium - {Mars - Uranus}
Morphics - {Mercury - Mars - Phobos - Europa - Pluto}
Neural Sensors - {Jupiter - Kuva Fortress}
Neurodes - {Earth - Lua - Erie - Derelict}
Orokin Cell - {Ceres - Saturn - Derelict}

Detonite Ampule - {Mercury - Earth - Lua - Ceres - Saturn - Uranus - Sedna - Kuva Fortress}
Fieldron Sample - {Venus - Mars - Jupiter - Europa - Neptune - Pluto}
Mutagen Sample - {Erie - Derelict}
Tellurium - {Uranus - Kuva Fortress}
Pigment - {Mercury - Venus - Earth - Mars - Phobos - Ceres - Jupiter - Europa - Saturn - Neptune -] [Uranus - Pluto - Erie- Sedna - Void - Derelict - Kuva Fortress}

{Grokdrul - Iradite - Maprico - Nistlepod}

{Condroc Wing - Kuaka Spinal Claw}

{Cetus Wisp - Breath Of The Eidolon - Eidolon Shard(Brilliant, Radiant)}

Metals - {Auron - Coprun - Ferros - Pyrol}
Minerals - {Azurite - Crimzian - Verido - Sentirum - Nyth(Heart Nyth) - Devar}

Note that you have to cut the fish that you catch, by that you go to Fisher HI-LUK in Cetus
Spoils - {Fish Meat - Fish Oil - Fish Scales}
Parts - {Charc Electroplax - Cuthol Tendrils - Goopolla Spleen - Karakina Antenna - Khut-Khut Venom Sac - Mawfish Bones - Mortus Horns - Murkray Liver - Norg Brain - Seram Beetle Shell - Sharrac Teeth - Tralok Eyes - Yogwum Stomach}