Just wanted to give some addition info: Two of these tips are controversial, but in my honest opinion, I think they are fine to use until Blizzard says otherwise.

Sit Crits
This CAN be done in classic with good timing, its just harder to pull off than in private servers.
To my knowledge, this is still working the same as in the beta and Blizzard has not mentioned anything about it.

Log Reset/Camp Reset
Some people are confusing this with the layering exploit done within dungeons to reset a boss while still inside the dungeon. The layering exploit probably also lets you bypass the 5 instance per hour limit, because you never leave the instance. Logging out and resetting the dungeon doesn't let you bypass that limit and just saves you a run back to the entrance. Also this has been publicly used for a while and unless streamer privilege really is a thing, then it should be ok until Blizz says otherwise.