There are several rules to keep in mind if one wants to win, and they are most crucial at the start of each misson.
Usually you will start out in the open where robots can shoot you. Hide under a girder or next to a tall rock or cliff or even into a dip in the ground as soon as possible.
2. Take time to aim
One of the lamest mistakes one can make is to aim carelessly or in a hurry.
3. Match trajectory up with trajectory down (for long range shooting)
4. Throw grenades about one inch short on flat ground or girders.
5. Watch the shooting pattern of the bots; after one of them has fired, and there's several other bots, that one is safe until it's turn comes around again, so you can move or ignore it for a while.
6. Leave stupid or blocked bots alive
Make them take up a turn while they shoot themselves on a rock or fly / bounce around uselessly. Gives you more time to go after the big ones with multiple shots from your team before they can wallop you.
7. Go stand next to a robot which just had his turn. Mostely you will take damage from other robots anyway, so why not let them shoot their own robot too. Standing directly next to cannons will also keep you safe for the cannons itself.
8. Flying Robots can only go so far and can get stuck in pits so dont fret about them go for the armored and cyclon bots
(many other tips or addendums to the above can be added here)