I`m 11 and I`ve been playing piano for almost a year, and I was wondering if there was a proper technique for glisses. Because whenever I do it I either cut up my nails real bad or hurt my hands. Any advice would be greatly appreciated.

Yeah, I try to avoid glissando and play a C-Major scale.
If I can`t then I use:
Right hand going up: the back of 3 and 4 finger
Right hand going down: cushion of 3 and 4 finger
Left hand going up: same as right hand going down
Left hand going down: same as right hand going up