1. Players usually bend their knees before initiating a forehand stroke, as well as turn their upper bodies away from the target. They then initiate the stroke by extending their hitting side leg, extending their hitting side hip and perform a spinal rotation towards the target. In high level strokes, that rotation slows down around contact, allowing the arm to catch up -- basically, if you keep turning through contact, you're not using the rotation of your body to propel the arm forward. That'S why top players face the net at contact on their forehand.
2. The so-called "wrist snap" on a topspin forehand groundstroke is a combination of many movements. Do know one thing, however: that combination of movement does not involve a whole lot of wrist flexion -- i.e., you're not slapping the ball as you would slap someone in the face. It combines a bit of wrist flexion, radial deviation and forearm pronation. Basically, when you start to swing forward, your wrist extends and performs ulnar deviation and there is a bit of forearm supination -- it's this violent movement you see in slow-motion when the racket starts lagging behind the arm -- and the snap in question reverses in part all of those movements around contact. After your follow-through, your wrist should be neutral and your hand should be in a fully pronated position -- i.e., your thumb is pointing down if you extend it.
A good tip on how to do all of those things right? Rick Macci's videos on youtube are indeed great videos. He makes things very simple. Performing a solid forehand is just a matter of putting your body parts where they need to be before you start swinging forward and knowing what to do once the ball is gone so that your racket behaves properly throughout the whole swing. He also keeps pounding this point that you need a short backswing because so many people get caught late and in fact loose power due to a bad preparation -- too big a swing is a bad thing and it's easy to make when only one hand is on the handle.
3. This one is a peculiar tip. Some people suggest learning about a 2 handed forehand first to help cement good forehand habits -- the limitations imposed by your second hand does force you to cheat less on proper mechanics and to work better. So, to know if you have too big a backswing, get your racket to the furthest point you take it and see if you could place your off hand on the handle on top of your hitting hand. If you can't do it comfortably because your body is in the way, your backswing is too big, period. With two hands, I can't break the plane of my body, sending my hands behind my back because my second arm runs into myself every time I try... So, it's a good indicator of how big a backswing you actually need.
