Originally Posted by WillyCañas
all players hit running forehands... some better than others (f.e. Nalbandian has a great running forehand).
I don't think you should spend time developing a running two-handed backhand.... work on your slice... which can be used as a great defensive weapon.
Here are my thoughts:
I agree with the post above. If you're still young, work on the slice when you're pulled out wide on the run. If you ever start playing very high level players, you'll be glad you did, as it will extend your reach, and it's much easier to hit when you're pulled side to side at full run. It will also help when someone hits an extreme kick serve out wide, which can be difficult to return deep with a two-hander.
Having said that, you also need to be able to hit the two hander on the run sometimes, especially if someone is going to close into the net when you're pulled out wide. In those cases, use the straight take back motion (i.e. no loop) with a short back swing (and possibly an open stance, if possible), almost a block type motion as you don't have time for a full swing. Maybe think of Agassi's short backswing (or maybe Coria or Hewitt) when he's returning or pulled out wide.
It's a difficult shot that is mostly timing, balance, and footwork. Have someone feed you balls to practice the shot. Start at the center line and have them feed you a basic forehand where you have to move slightly to the right. Then have them pull you way out wide with a feed. Hit the shot as noted above, and make sure you move back toward the center as quickly as possible to get ready for the next shot.