They actually aren't as easy as they look, at least to do them right. For nose presses, the key is to get on the rail with the rail under your toes, not midsole, then lean forward as you pull your feet back, timing is key and a little tricky to get used to, once you get into position (with the rail past your toe piece) it's all about keeping your balance and making sure not to slip out of the rail, try and keep your eyes on the rail while look straight down (so if your eyes could shoot laser beams they'd make a perfectly vertical line straight to the rail or edge of the box), then at the you have to pop off the rail (like a nollie) and turn, you can't really just slide off very easily. For tail presses, same as the nose (but opposite), get on the rail with your heel over the rail then push your feet out while sitting back on your tails - the farther you go out, the lower you have to sit, you don't need to look as much with these so just focus on the end on the rail like normal, then pop off (like an ollie) and turn. BE WARNED - you will most likely catch your edges a lot while trying these, so learn them on a lower feature. The reason you catch your edge more is because it's harder to keep the front edge tilted up while pressed so it tends to catch, leading to a sudden stop of your skis on the rail, sling shooting you forward and into the ground. For both of them, try to keep your arms to your side, it'll help a lot with balance, use your body more to balance than your arms, it has more mass so it'll do better equaling everything out, and it'll look better. Good luck, presses are super fun, and when done right, the look SUPER sick.
~WAKIN' UP THE NEIGHBORHOOD TONIGHT!~