As most guys/girl said, commitment is a big factor. If you want to get comfortable on 1s and 3s scared of the park kickers, try small jumps from the side of groomers.
For 3s, the key is really your pop and head/shoulders: you don't need a lot of momentum for a 3, even for a 5, so don't focus on trying to spin your body too much, you'll go off axis. Pop as high as you can at the lip, and more importantly pop up (not front, back, or sideways) the movement of your shoulders/head needs to be flat, so focus on looking behind you turning your head, but not down or up.
You can prep with your arm before popping but make sure you don't start spinning before you're actually airborne (again, with bigger spins it's not the same, but with 3/5 it'll make you easily go off axis, reason why big spins not corked or flipped are quite rare/hard). Once you get more comfortable, focus on popping, starting the spin and tucking you knees up. Once you feel that it flows well, you can try adding a grab, japans are pretty easy, then safety then mute. Or tail grab too, which can actually help you straighten you axis if your going backwards a bit.
For rails, just get comfortable board sliding boxes, then tubes if your park has them. They're essentially the same, tubes are just not as sticky and you need to think "lighter, smoother" on them. If there are only side entry rails at your park, make sure you don't come at an angle, or you'll slide off everytime. It's hard to do it fast at first, but try to hop on, lifting your front ski first and doing a quick 90, and keep looking at the end of the rail. Don't think of putting more weight on the back or on the front ski, just think light and smooth, almost life if you were skimming the rail. As you get more and more comfortable, you'll come to know how to apply more pressrun where it feels right really.
Good luck bro!