Welcome to the guide! You should unlock most achievements if you play the game thoroughly (look at and interact with everything, complete all conversations), but the below guide should help you catch the more obscure ones.

A few of the achievements are mutually exclusive - that is, performing an action that leads to one achievement being available can lock out getting other achievements in that playthrough. I'll try to point out where these occur, but given the short length of the game it won't take you very long to replay the game to get any missed achievements regardless.

Commence your mission on board the HMSS Imperialise!
Unmissable, story related.

Look intently at Sub Lieutenant Jones
Look at Jones five times, until he reacts saying "Stop looking at me, boyo. You're starting to creep me out."

Examine the Gravity Simulation Switch
Examine the Gravity Simulation Switch on the wall just outside the cockpit.

Attempt to mix washing up liquid and tea
Once you've filled either mug of tea using G.E.R.T.E.A., try to combine it with the washy liquid (also in the kitchen, on the counter).

Talk to G.E.R.T.E.A. about British villains
Speak to G.E.R.T.E.A. five times, until you mention Alan Rickman.

Give Sub Lieutenant Jones English's tea
Give English's mug of tea to Jones instead of Jones's own.

N.B. if you do this you cannot get the Call Autoglass! achievement in the same playthrough, so I'd recommend you save before giving Jones any tea, then reload once the ship's controls fail to try the other path.

Crash into ejected fuel cell when at the controls of the HMSS Imperialise
When Jones hands over control of the ship, flick the black switches at the top left until a voice says "primary starboard fuel cell jettisoned", then move the throttle at the bottom left forward to hit the fuel cell. The order of the switches is random each time, so it could be the first one you choose, or the seventh.

N.B. if you do this you cannot get the Sharing is caring achievement in the same playthrough, so I'd recommend you save before giving Jones any tea, then reload once the ship's controls fail to try the other path. You must give Jones his own tea, rather than English's.

Locate the paperclip
Unmissable, story related.

Ensure no one can erase the driver
Once you've loaded the driver onto the floppy disk, re enable the write protection.

Wake up Sub Lieutenant Jones
Unmissable, story related.

Break a sweat when using the treadmill
When trying to get below deck, once English has gotten stuck use the treadmill in the sitting room until you stop and say "it's just like exercising at the gym, albeit without the judgement of others".

N.B. if you do this you cannot get the What a thrill! achievement in the same playthrough, so I'd recommend you save after English gets stuck going below deck, then reload once you've used the treadmill to try the other path.

If you use the strategy for gaining the What a thrill! achievement you won't be able to get the Bubbles! achievement later in the game, as that requires you hold onto the washy liquid; follow this path instead to be eligible for Bubbles!

Use the ladder like a boss
When trying to get below deck, once English has gotten stuck use the washy liquid on the hole to below deck, then climb down.

N.B. if you do this you cannot get the Cardio, bruh achievement in the same playthrough, so I'd recommend you save after English gets stuck going below deck, then reload once you've gone down the ladder to try the other path.

If you use this strategy you also won't be able to get the Bubbles! achievement later in the game, as that requires you hold onto the washy liquid; follow the path for the Cardio, bruh achievement to be eligible for Bubbles!

Crush a table top football player
In the sleeping quarters, walk around on the table football game until you break one of the players.

Find the replacement motor
Use the motorized screwdriver to open the locker in the sleeping quarters.

N.B. if you do this you cannot get the Premium Engineering achievement in the same playthrough, so I'd recommend you save before opening the locker, then reload once the ship's controls fail to try the other path.

Locate the French camp while driving the Beagle Two Too
Give the motorized screwdriver to Jones to fix the Beagle Two Two. Once you're in control of the Beagle Two Two look around until you see the Statue of Liberty, carefully head down the ramp beside it (crashing will break the Beagle Two Two), then follow the path to the left until you reach the French camp.

N.B. if you do this you cannot get the She's behind you! achievement in the same playthrough, so I'd recommend you save before handing over the screwdriver, then reload once you've found the camp.

Examine all the rocks on the planet surface
Quite simply, examine all the rocks once you land on the surface. These are located:

• almost directly in front of the ship
  
• behind the ship
  
• to the left of the ship
  
• to the front right of the ship
  
• two directly on the path to the French camp, once you've gone down the ladder

Summon the Power of Greyskull to distract Antoine and Pierre
Use the "By the power of Greyskull!" dialogue option when first speaking to the French colonists.

Maybe it was earth all along?
Once you go down the ladder on the surface, walk left up to the Statue of Liberty.

Observe Schrödinger's cat both alive and dead
In the ship's lab, touch the box to either hear the cat meowing, or silence. Then leave and re enter the room, touch the box again, and hear the opposite.

Put frogs to sleep
Unmissable, story related.

Fail to catch a frog even when they are asleep
This relies on you having completed Lullabies to paralyze to put the frogs to sleep. When using the claw grabber, fail to grab any frog on your first try.

Save game progress using the typewriter
Use the typewriter in the ship's lab to save your game.

Acquire a second block of cheese
Combine the whole (non Swissed) cheese with a frog, then offer it to the Frenchman. Once the cheese and frog have been destroyed, speak to Jones and ask for another piece (and frog, to complete the puzzle).

N.B. it's possible to miss this achievement if you accidentally give the Swissed cheese to the Frenchman first.

Place washing liquid inside washing machine before it's activated
Before disabling the security system permanently, use the washy liquid in the washing machine while the power's off.

N.B. it isn't possible to get this achievement if you followed the steps to get the What a thrill! achievement, as you will not have the washy liquid. Instead follow the steps for Cardio, bruh to keep the washy liquid.

Complete Her Majesty's SPIFFING: The Empire Staggers Back
Unmissable, story related.