Take some lessons! I had some this winter, cost me 160$ for 10x90min course with a teacher, helped me so much. If you can't i'd say frontflip, misty 5 and side flip are the easiest.
Well after I learned learn front full it realy helped me. the way I learned it I had to go half a front flip then start rotating while finishing your front so I did most of my rotation with my feet in front and my rotation axe to the horisontal... Its not a cork but you get the feeling and a better general aerial skill to like know where you are and feel better in the air. It felt was easier and safer to learn cork after!