Basically what Skribs said
The only thing I'd add is that you don't have to turn much. Remember that you
have a roughly 180 firing radius, so if you make even a quarter turn in mid air and fire, it will make it easier to turn back.
A lot of people try to spin in a full circle when jump-shotting, but that's just making it more difficult (and dangerous) than it needs to be.
What level is your hunter? There are some really good mobs to practice on in your upper 50s, but if you're lower than that the best thing to do is to find a mob a few levels higher and try to pull them back to town (for example, if you're 15... try to pull a LV 20-22 mob from the WC area back to Crossroads). This will help you get an idea of how best to do it.
The other viable way to get experience is... (Dun dun dun) PVP. I find world PVP
is especially effective in this training if you're on a PVP server... since it's not planned and may be unexpected.
Hope this (70 troll Hunter, blackrock) SV
--Penance (70 Blackwind Sabrecat)
--Seraph (62 Ghost Wolf)
--StoneGmork (57 worg)