Some random tips I've learned since noobing it up as an engineer. Apologies if some of these are obvious:
1) While in lift pads, you can duck to go down quicker, and jump to go up faster. In fact if you hold down jump, the yellow lift throws you really far in the air, you can reach awesome camp spots this way
2) Lift pads make you immune to fall damage for 10-15 seconds. Simply skirt through a lift pad, now you can safely jump all the way to the bottom of the base with 0 fall damage.
3) You can sort of control jump pad trajectory by moving mid air. If you hit a jump pad backwards it seems you can fall really short of the landing pad.
4) Using a drop pod and trying to land on a tiny tower or tree branch? Center it, and make sure you STOP changing directions a good 3-5 seconds before you land. Otherwise momentum throws you way off your target once you land.
5) Dont bother loading out the engineer ammo pack, use that spot for tank/prox mines. Simply pick your turret and hit 'b' to switch to an ammo pack.
6) Turret is sniper bait, don't use it in the open. But it makes a great ladder to get to spots only light assaults can. In south bio-dome, I love using it to climb the trees.
7) Underbarrel grenade launcher is still a bit bugged. If you shoot it as fast as possible, you will stop restocking ammo no matter how many ammo packs you sit on. To prevent this, after you shoot and auto reload, wait until you hear the restocking 'click' (and see 1/1 ammo). It only takes an extra second, but nothing worse than reigning hell down on people with grenades in the perfect spot (ie Bio dome tree =D) and bugging out.
8) Suck it up and get at least a few ranks of mine guard on your Sunderer. It's ridiculously cheap for what it does. Stop my suicide engi mining runs in it's tracks. A fully mine guarded Sunderer takes SEVEN mines to kill.
