I'm here to say cork 3/5 and cork 7s are very different. If you want cork 3s go on your tramp and spin a few warm-up 3s in your natural spinning direction. Then you must do a 3 with trailing safety (if spinning left, grab with right hand). Once you have that down start bringing your ear to your shoulder. The key is to pull your foot up with the grab and tip your head(left ear to left shoulder while spinning left) but allowing your shoulder to dip with your head so that at 90 degrees your trailing knee is up by your chest and the lead leg is straight and parallel with the trailing arm. As you continue slowly spinning you want you to pull the trailing foot up with a kicking motion that aims to the roof and behind you slightly. At basically all points in the trick, your lead leg should be straight as an arrow while you rotate around it like a top. At about 270 your trailing foot should be pointing to the roof and slightly back from the starting point, your body should be parallel to the ground, and your lead arm and leg should hang down to the tramp. At this point in time let your trailing foot fall as you release the grab and spot the landing. With regards to starting the rotation in the first place, I would like to put emphasis on sucking your knee up towards the opposite shoulder and then dipping. It's important to wind up and spin much like a normal 360 while quickly focusing on the grab as it is the padlock on the gate to cork 3s/5s. I will include a video for your eye's pleasure.
https://www.newschoolers.com/videos/watch/876013/LGAQ8600-1--MOV
Once you learn it on tramp it is actually easier on snow because the lip will aid in the dip.Its the same principle of how the jump does 1/8th of a backflip for you. Add a little carve and you should be steezing dog.
**This post was edited on Sep 20th 2017 at 5:54:18pm 
