My best advice would be just keep trying them. I never lip slide anything and then I decided to start trying some today and for some reason they just worked. Basically the trick is to come into the rail at a bit of an angle pop look at the rail and make sure your tails get over it should kind of just work as long as you get your tails to clear.
Come in at a pretty good angle to the rail then pop and focus on bring your tails up and over it. Start by trying it on something low risk and not too high up and you should be able to get it after a few tries. The hardest part is getting over the initial fear and awkwardness of it, but aside from that the mechanics of it are pretty much what you'd expect
Lips sliding is my favorite trick and it is so fun if you get it down. Just give yourself a little more room and speed to get your tails around while popping a little harder than you normally would. Just focus on driving those noses down after that pop. I like to picture myself backing into the rail until I feel it on my underfoot to get an idea for the feel. Then.. just level out your skis and grease it.
Once you get lips, try doing lip slides to back 2's. They're probably one of the "flowiest" and most rewarding tricks in the game, IMO.
yeah i tried learning them by going parallel to the rail, and that does not work. As stated already, I tried going at the rail at an angle and it worked SO well. just remember to whip those tails around. super super super fun trick, and looks tight
approach rail with significantly more speed but not booking. come at a greater angle and aimed to pop a little farther to the side of the lip than normal. pop REALLY HARD! keep your tips down and come down onto the rail so you land on your toes a little to keep yourself from sliding over the rail. scissor appropriately to come off however you want. stomp.