Your First Grabs
The first grabs you do should be either a backside or frontside indy. This is because it's easiest to grab with your trailing hand if you want to land forward, and indy grabs are back hand, toeside - a natural non-tweaked position. Look at the sequence of Scott Jobe doing a backside indy. Note that he launches cleanly off the wake, pulls his board up (look how bent his knees are) to his hand for a firm toeside grab, pokes it back for a little extra style, then holds onto the board a little longer before letting go and setting the jump back down. This is good technique. He cuts all the way through the wake before grabbing, gets a firm grip on the board and holds it long enough for you to tell it was a grab, keeps his head up and body on a level plane - and he even twists and bones it out for extra style.
Once you get basic indy grabs like this, you should try some melans (melancholy). When doing a rear-hand grab, like a melan, the boat naturally wants to pull the side of your body that is holding the rope toward the boat. So in order to keep a melan grab under control, you have to keep the handle in close to your body. In the sequence of C.C. doing a backside melan, he cuts in progressively and by Photo 3 he has completely cleared the wake with both hands still on the handle. This is good. You can't even tell he's going for a grab at this point. Then, in the air he pulls his back leg all the way under him, grabs heelside and pokes out his front foot for style. Look at how he doesn't bend at the waist much from the time he is cutting through the whole maneuver. He keeps his head up and keeps his body on axis.
After you have these grabs wired, you might want to try a frontside melan to fakie, or an indy half-cab, which is just coming in fakie, grabbing toeside, then landing forward. Remember: On rotational grabs, whichever foot you are going to land forward with, leave that hand on the handle. For instance, if you take off right foot forward, and let go with your right hand, it will help your rotate on an indy half-cab.