First you need to learn your own weaknesses:
Your head has most armor. A hit will only cost your about 20. Legs are more vulnerable and you get hit for around 33. Your butt is weak and things will hit you for about 60 to 70. The vent under your butt if your absolute weakpoint. An Armor weapon will do about 90 damage there and Infantry can hit you there with normal weapons for approx 1 dmg each bullet.
Should your Walker ever touch the 15 health mark it will trip over - even if it is repaired up again!
A good walker driver looks out for cover for his legs. If only your head sticks out somewhere a normal supplybox will keep you up vs one enemy engineer easily.
The worst foe of a walker is EMP and Orbital Strike combo. If it hits you on the head you will get destroyed unless you have some suicidal engineers right under you. When you stand still and get repaired always look down on the floor and keep holding SHIFT. You can see the ground "sparkling" if there is EMP incoming - quickly press forward to make a step out of the central point of the strike and survive.
Right after there are EMP Grenades and Motion Mines. If you get stuck in a good EMP Grenade trap you are pretty much helpless - it happens to the best of us. Do not bail out just pray for your team to do something. Motion Mines will follow your walker and if they detonate will do anywhere from 20 to 80 damage. The Motion Mine Bait unlock makes so much difference when driving a Walker. After you practised some Walker you will get to know the "common" Motion mine spots - so you dont walk into them.
If you fight an enemy Rosch shot your Rockets at it. If it is still not dead aim for the left side of the Rosch - if you shot onto the Barrel the splash damage will slowly kill the gunner in it.
Your walker can run forward about twice as fast as you can walk backwards. Use this to your advantage and always keep an emegency path in your front so you can escape quickly if there is heavy fire incoming instead of having to crawl backwards and being an easy target. When your shieldcharge is down and you took even a sliver damage it is time to retreat and repair!
Try Squadding up with a good Squad and escort it with your Walker. You can help them as they can help you. You will scare the APCs away that try to eliminate them and they can take care of people EMPing you and recons rushing you. A good Squadleader calling in Supplies for you is always sweet. Sometimes there is also a nice gunenr to be found who will happily hop out to fix you up during the round.
Try to stay alive. Even if you do not get a big killscore it will still focus the enemy team on your walker. Not every tactic has to award "points" to be effective
Just practise the Walker. Some maps have a hugh respawn time like around 5 minutes on Camp G - not so suited. But maps like Highway Tampa have lots of walkers with a better respawn time - shouldnt make you feel so bad about helping your team when you should go down.
Driving a Walker and keeping it alive can be one of the most exciting things in BF 2142. When you accompany your troops you will be their "Avatar" and give them strength and willpower!