It depends on the difficulty you are playing, but note that faster is not necessarily better.
If you are playing Easy, Normal or Advanced difficulties, then by all means the best thing to do is light him on fire with a Molotov cocktail or gas can and then get as far away from him as possible. Make sure you can get to an area where he can't hit you with rocks. You can shoot rocks out of the sky with your weapons or the Gatling gun, however.
You also want to make sure that the Boomer does not vomit on you when the Tank is around, because it's harder to keep away from him when the horde swarms you.
If you are playing on Expert difficulty, never, ever, ever light the Tank on fire! In Expert difficulty, the Tank runs much faster when he is on fire and can outrun you when you have health in the green (60 or higher). If your health is less than 60, you're pretty much guaranteed to be incapacitated. Instead, you need to learn how to strafe and dodge the Tank so that he's less threatening. If you're playing with bots, it's much harder to survive a Tank encounter, but with human players, you need to focus on two things:
- Make sure you don't forget to keep moving. Lots of players forget this, stand still and shoot at the Tank until he's right up on them.
- The Tank only targets one player at a time. Learn how to tell who he's targeting, then let that person skirt the Tank around while the other three Survivors shoot at him.
Lastly, you can use oxygen tanks, propane tanks, and even an exploding Boomer to cause the Tank to stumble for at least 3 seconds, which is a great opportunity to get in some cheap shots.