Personally, I would only do instances when you're well rested. Then do all the kill quests you can find. The only reason I've ever grinded an instance was to a) farm a certain drop (or multiple drops for my shamans) or as I'm doing currently b) Emblems and Shards (40 shards away from 5 mammoths, woot!)

Do collections if you know it leads to a bigger chain, but for the most part collection quests suck.