This mainly comes as a healer: Learn the mechanics of the fights, and pay attention to what's going around you. So many people just focus on whatever their rotation is, usually trying to squeeze out just a little more extra dps. And then they find themselves on fire, falling off a cliff, missing an interrupt, whatever.

Focus on staying alive. You can't heal, tank, or dps if you're dead. The nitty gritty of optimized shit doesn't come into play unless you're doing the highest end-game progression type of stuff.