Blood boil’s scaling is a bit odd, and until level 80 it hits like a truck. At 81 you get Outbreak, which makes it easier to apply diseases to your targets.
Stack mastery, keep diseases up on your target(s) at all times, rune strike to dump RP/generate threat. Death Strike is your new best friend. You can either use it to build up a large blood shield, which absorbs incoming damage, or to heal yourself after you receive a large amount of damage (blood shield is a function of incoming healing and mastery which is why we have ridiculous amounts of it.)