Jet mode:
The weapons in Jet mode are significantly less effective than the weapons in Walker mode. Couple this with the fact that Jet mode does not allow the Shield to generate. Only use Jet mode when you need to blow something up or kill a Fighter (or any other air units such as bombers, landers, etc.) in the air. Stay on your side of the battle as it will be nice to have a helping hand when things get rough. Avoid using all your energy while in Jet mode; when you land you will have no shield. Repair Pads are your friends — use them.