Wash the inside of the grips with soap and warm water and let dry thoroughly. At this point, the grips actually become a little tacky, try not get any dust into the grips after this.
Slip a nickel (if you're American) into the grips ends so it won't rip through during a crash. Clean bar with alcohol first and rub a tiny bit of alcholo on the tip of the grips and the bar, slide grip on. If it won't go in all the way, don't twist it. Pull it out and use a little more alcohol. You kind of have to play around with how much alcohol to put on the bar.
Ourys are my favorite, easy on, easy off. To remove, just roll it off into the shape of...for the lack of a better term, fresh cond0m from a packet.
Hairspray never works for me either.