For the first question, it all comes down to a good steady pop and repetition. Make sure your knees are bent and your legs are just under scheduler width apart. Have a solid amount of shin pressure and pop straight up evenly off your feet with your hips and legs. This should result in very stable position in the air. Once you are comfortable with the sensation of being airborne, slightly bend your legs up. Focus on the pop not the grab. I used to just focus on the grab and pop unevenly because i was trying to get my ski in the right position..There is really not much more to it. It will take a few times but i promise it will come natural to you soon.
for the 360, https://www.youtube.com/watch?v=D5dwEXPxvDA
honestly the best explanation out there. Jake muller is a godsend i swear. He answers your question perfectly.. good luck!