Shuv it help

When i shuv it i always slid out or it doesnt get all the way around like its a 90.

land more on your toes so it doesnt slide out, find your balance, just takes practice. for the rotation, try shuving a little harder and if that doesnt work give it a little extra push with your front foot. should help.

scoop your back foot down and behind you towards your fornt foot. do not spin the board with your front foot. also, keep your feet apart through out the trick. if you bring them up and together you will land with your feet together and bounce off the board on landing

If the board is only going 90 try to do more of a scissor motion with both of your feet. My experience has been that the board does not get a full 180 rotation when I am trying to spin it with my back foot only.

Also try to keep the handle in close to help prevent sliding out.

Put your feet in the ollie position (back foot close to the tail, front foot like 5 inches away from the nose). Ride outside the wake. Both HS and TS shove-its are possible. Distribute your weight more to your back foot than in your neutral riding position. Bend your knees and keep your upper body upright. Hold the handle only with your lead hand. Now perform the trick by popping the tail like you would do for an ollie, but as you're popping, whip the board around with your back foot. Really focus on mainly using your back foot for performing the trick. This is key to sticking it and getting it consistant.

I guess different things work for different people, I have had experiences in the past where I wasn't riding away from shuvs and found it was because I was riding with more weight on my back foot and trying to perform the trick using only my back foot. But again what works for some may not work for others.