There is a lot of good advice here already so I'd just like to mention the tank holds responsibility in speed runs too. Nothing annoys me more than a tank that pulls everything up to the first boss, uses one minor cooldown (if any at all), and calls it a day. If the tank expects you to speed up the kills by spamming Holy, they better be using some big cooldowns (looking at you, paladins who don't use Hallowed Ground) because I can't DPS when I have to babysit the wild roller coaster that is their hp bar.