Yeah, don't use one.
But if you do... Try to go as vertically as possible. Otherwise the bottom can kick out, the top can kick out, or the whole thing can fall over sideways taking the Jeep with it. Don't ever get under a vehicle that is supported by only a high lift. Basically just have some common sense and be careful. Always assume it's going to fall over or do something violent and keep yourself out of the way.
It's a shame they're so damn useful, because I really hate using them. I also recommend a small bottle jack for changing tires.