Snake it. What comes out will be disgusting, so tough it out. Plenty of videos on youtube, doubtless there will be one for your particular tub style.
In college I often used a piece of clothes hanger wire twisted into a tight corkscrew, it worked but was harder to use. Reach was limited, but the clog was invariably within reach.
Afterwards, go to the store (hardware or walmart) and get a drain filter. Its a metal mesh dome of sorts that fits over or in your tub drain. It gets the vast majority of the gunk that would otherwise clog the drain. Clean it off with a shake in the trash can, wipe with TP, etc and put it back in use.
Using liquid soaps and shampoos will reduce the clogging tendency, vs using bar soaps. Mostly though, you have to keep the hair from going down the drain.