Using hairspray is just part of the morning routine. You do it over and over in the same place, day after day. Before you know it, you have a buildup of hairspray on the wall behind you, on the mirror or even on the floor. The sticky mess will start to attract dirt and grime, so it's a good idea to get it cleaned up on a regular basis.
Wet a rag with rubbing alcohol.
Wipe over the surface with the rag. This is safe for just about any surface, including wood and glass.
Dampen a sponge with ammonia if the surface still feels sticky. Rub the sponge over the area to clean it. That should get all hairspray residue up.