basically heres how i learned to do it...
begin with a safety 3, pop and take off as you normally would, reach down for your grab at around 180, your probably trying to grab immediately which is a mistake. at first it will be shitty, like a litte touch, or a boot grab, but after practice start holding it as long as you can, almost landing on your hand. then you can add it too larger spins, and sicker grabs. blunts, stalefish, mute etc...
another thing that helps, and is fun as fuck, is just straight airing shit and holding tweaked grabs for as long as possible, like hold a tweaked stalefish in the air for a long time, it will feel scary and weird at first, but you get used to it, and then you can just do it without looking, and eventually bring it to spins.