What not to do. We have a player in our club who came in and since he had no opponent at the moment took out some photocopy pages of chess diagrams of tactics. He sat there and moved the pieces around trying to find the combination that worked. When i walked over to see if i could solve it, he looked up and said, "i think i have it, but i'm working on the right order of moves." he took the e pawn with a bishop, then moved the pieces around, taking them off the board, replacing them, etc. I said, Who's going to let you do that during a game?"
"What do you mean?"
"You should sit on your hands and move the pieces around in your head. That's what you do during the game."
"But this combination is about eight moves deep."
"If it's too much for you now, the exercises are too hard." I told him, "Start with one or two movers and work your way up."
"But my teacher gave me these!"
I didn't ask him how much he was paying the teacher. I didn't tell him to get his own book of tactics puzzles, with some a lot simpler than the one he was doing. If he didn't pay his teacher, he could probably buy a bunch of puzzle books.