The easiest way to make a three-star score on a stage is to go for as many kills, and/or to hit as many robots at a time, as possible.
Easiest way to make a kill on a robot is to blow out all of the land from under them, causing them to fall to their death, or to use an explosive to knock them to their death.
Experience points will allow you to unlock new weapons and armor, and you can use those rivets that you earn to upgrade and become stronger.
Upgrade the parts that you already have, instead of buying same-tier parts, and save your rivets until you unlock the next tier of parts.
After you launch a weapon you’ll have about 3 to 5 more seconds left to move before your turn ends.
Jumping accurately can be difficult to figure out, but you can change directions in mid air, allowing you to land on platforms and get into spaces that you otherwise would not be able to.
Watch out for the point drops and for weapons drops on the stages that you play.
Landmines are the cheapest, and they do more damage than rockets, making them an excellent weapon to stockpile.