Let me show you guys how you guys could achieve 100% on this game.
Just follow the steps below.

If this guide was helpful, give me a bit of appreciation by rating my guide and rewards. :)

Achievements you will get if you just play the game.
Mostly you will get these achievements if you just let the game flow.
I will also write estimated time to get the achievement.

- Traveler : Walk 10,000 steps
(est. 3 hours)

- Walker : Walk 15,000 steps
(est. 5 hours)

- Ballet Dancer : Walk through the base full of colonists (Part of main mission)
(est. 30 min)

- Miner : Step on 10 land-mines on one level (Just avoid mine on mission)
(est. 1 hour)

- Alien Invader : Destroy the citizens of Thuaaghi Settlement with Death Ray. (General side missions)
(est. 3.5 hours)

- Rebel : Refuse to obey orders (Scientist side missions)
(est. 3.5 hours)

- Best friend : Kill your best friend (kill Kessie)
(est. 2.5 hours)

- Alien : Kill 3000 natives (literally)
(est. 4 hours)

- Engineer : Research 25 upgrades (literally)
(est. 3 hours)

- Warrior : Destroy Dr. Chivington’s walker (Be on general's side and finish the game)
(est. 4 hours)

- Scientist : Destroy General Garay’s walker (Be on scientist's side and finish the game)
(est. 4 hours)

Some achievements will be hard to achieve than the above but it is achievable.

- Pacifist : Complete any level with the enemies without making a single shot. (Do this on second mission since the enemy is weaker)
(est. 10 min)

- Godzilla : Squish 3 colonists at one step (It means you have to stump on three civilian in one go - yes, you will fail the mission but at least you get the achievement)
(est. 15 min)

- Asphalt paver : Squish 5 enemies at one step (You can do this at an later stage where enemies storm at you in group)
(est. 2.5 hours)

- Tankman : Mount level 5 cannon on your walker (Max the cannon and equip)
(est. 2 hours)

- Zen-buddhist : Walk through the any level with the enemies in economy mode. (similar with Pacifist but at a hard-core mode and has to be in economy mode)
(est. 20 min)

- Heavy Weapon Guy : Mount level 5 machine-gun on your walker (Max machine-gun and equip)
(est. 2 hours)

- Rocketman : Destroy 8 enemies at one rocket salve (Use max rocket launcher at an later stage)
(est. 2.5 hours)

- Alchemist : Paralyze and smash 8 enemies at once (Use gas launcher and blast them!)
(est. 2.5 hours)

- Steeplechaser : Complete the initiation ceremony for 3 minutes (On the scientist side mission, complete the ceremony mission in 3 minutes, don't stump on the natives!)
(est. 3 hours)