This Achievement is unlocked once you have completed all of the Sub Goals in the Single Player Campaign missions.
Each Campaign Mission has 4 Goals attached to it, 1 Main Goal and 3 Sub Goals.
The Main Goal must be completed whenever you do a Mission, and the Sub Goals are optional.
You do not need to complete all 3 Sub Goals whenever you attempt a Mission; you can re-do Missions with specific Sub Goals in mind and you'll be fine so long as you also complete the Main Goal.
On the Campaign Menu you will see a green checkmark beside a completed Mission that you have not completed all of the Sub Goals for, and a gold checkmark beside one that is 100% complete.
Most of the Sub Goals are pretty simple or self-explanatory, but a few notes can be found below:
Most missions that require you to collect a Vital Crate will have a Sub Goal to defeat all enemy worms. These missions do not end after you have eliminated all enemies, so don't worry about having to collect the Vital Crate and secure the final kill on the same turn.
The hardest Sub Goal in my opinion is to "Keep all of your worms alive" in "Tsarface" (the final mission). What worked for me was the following:
> On your opening turn, have Worm #1 collect the Crafting Crate inside the building you spawn above, then use Switch Worm to control Worm #3. Move Worm #3 to the lower left side of the building interior in order to avoid the enemy sniper.
> Craft an Industrial Electromagnet on your enemy's turn.
> On your second turn, use your Ninja Rope to scale the building on your left, and take control of the Tank. Get out of the Tank and use Fire Punch to kill the worm that occupied it.
> On your third turn, group up with the other worm inside the building you spawned upon and use the Industrial Electromagnet (Repel Mode).
> For the next few turns, focus on digging towards the satellite with the Blowtorch in order to get the OMG Satellite.
> Use the OMG Satellite to kill the sniper. If you aim it leftwards you should get an easy kill and do notable damage to a number of enemy worms along the way.
> Throughout this battle make sure you keep crafting a spare Electromagnet to replace your existing one which will expire. The enemy likes to use Bunker Busters and is quite skilled with the Bazooka.
> Dismantle the Sheep as soon as you unlock it, and use it to create a Bunker Buster or Airstrike when a kill is possible with either.
> For the remainder of the battle be careful with your placement and deal damage whenever it is safe to do so. You may want to run the clock down and win via Sudden Death if things get difficult.
Other than that, simply take your time, learn how the various weapons work and you'll complete all of the Sub Goals with ease.
Note: You do not need to complete the Bonus Missions (part of the All-Stars content) to unlock this Achievement.