Waiting till 180 to grab is a biggie. But you cant rush grabs definetaly not your first spin grab, you gotta keep doin them till you get some air awareness. Try doing bigger jumps. Then at 180 just kinda play around, try pulling your legs up, or kicking your feet, just dont forget to look for your landing. This way you go from just doing it to really experiencing your airtime hence "air awareness".
Also when your trying to pull of harder grabs they can throw you off balance and it takes some practice to get used to it. A super good and fun way to get the hang is to do those straight air back scratchers