As BM you want to be using Arcane (and Multi/Aimed if you have mana and depending on spec). Macro in Kill Command to all of your main shots, that way you don't have to remember to trigger it.
Rapid Fire is a long enough cooldown you don't need to keep it on your main action bar, instead put it with Bestial Wrath, any racial attack boosts, and your trinkets. It's up to you whether or not you macro any of this together, since some cooldowns play nice and others are just weird lengths relative to each other.
You can often get away with not using Hunter's Mark at all if there's another hunter in the group, but since I don't trust other Hunters I macro it into my pet attack command so I have one less button to worry about.
Anyway, If I remember correctly, the BM priority list is something like this:
Kill Shot -> Serpent Sting (if not applied) -> Arcane Shot -> (Multi/Aimed shot) -> Steady Shot