How to prevent ingrown toenails?

I got an ingrown nail once because of how i trim my toenails. The smaller ones aren't really a problem, but you have to be careful when trimming the big ones. Since the nail really curves down into the skin, you need to make sure you've cut it all the way down, not leaving any jagged edge. If you do, the jagged edge will eventually grow & get embedded in the skin, causing an ingrown nail.