There's really not much to bair. I mean its a great move, but its properties are for the most part, centered upon racking-up damage, its projectile defense is pretty promising as well. So its good to just throw it out there for some quick ****.
Retreating bair's create a wall of 'near-un-punishable' priority, and its low cool down can promote abuse, which isn't always bad, especially if your shield pressuring. You should mix up bair approaches with empty SH's, SH's, Full Hops, and FF's. With full hops you can double bair,
FHDB (lol, like Falco SHDL?). But yeah, with a double bair out of full hop, you can approach with one bair and retreat with another, or double jump and mix-up some more. Retreating turtle to shrug the ending hitbox can lead to dsmash, fsmash, or even aerials.