For Tank, I'll also add that hitting things that are movable by the Tank/Special Infected (cars/forklift/trash dumpsters/that goddamn yellow thing everyone uses to block shit) will reset your Tank control timer. It's extremely good for going up against survivors that would rather wait for you to rush them like a moron.
Ex. The car at the bottom of the stairs near the safe room on No Mercy 1. If you get the safe room spawn, and the survivors are scared to come down, hitting the car resets the control timer (and will probably net you an incap if you're on the stairs).
Also, the super secret Sigel tank strat: Hit & run. The problem I see with many Tank users is impatience, and thinking that the 'roids make them invincible, which they don't. Set yourself up with some cover (open space = dead tank), and come out fast to whack a survivor, then run back to your spot (or, in the case of No Mercy 5, run in from one side of the radio room, hit someone, and run out. Make them think about what side you'll come in from next), rinse and repeat. This may seem like elementary shit, but you'd be surprised at how well it works, and how few people do it. Get tank, get yourself behind a corner, or a car, or a tree (I'm not even fucking kidding, Blood Harvest 3, ask about me), and start screwing with their heads. Many people here can attest to my full team incaps just using this simple strategy.
Tank = Mid Tier. Hiding Tank = High Tier. Tank with Mindgames = Asura Tier.
One more small tip: The tank can't run faster than/catch up to survivors until they are in the yellow or lower, so don't waste time and life trying to chase someone who's in the green, while they just backpedal and shoot you.
General:
Anti-Tank: Auto Shotgun. Holy shit, does the auto shotgun shit all up in his Cheerios. I especially rec. this for the tank spawns on No Mercy 5; A full team of Survivors with auto-shotties will kill a tank from full HP before he can even hit anyone.
Boomer: Think about where you set up. If you vomit/explode on them in a spot with an easy choke point nearby (e.g No Mercy 2 train cars), you'll do little to no damage. Make sure you get them in a spot with lots of zombies nearby, that will let the Horde do what they do best: surround someone, and hit them from all sides. Also, the boomer is great for just the general disturbing of shit. Everyone's first reaction to getting vomited on is to wildly mash melee, so work with your teammates to drag/pounce the survivors that aren't vomited on, while the ones that did get hit can't move due to the Horde.