Depends, for correspondence chess or live chess? Also what kind of live chess, blitz, quick or long time control?
calucations
Sort:
From my experience you improve at long time control by not playing blitz and you usually get better at blitz naturally by getting better at long time control. Back to the question on calculation...it is a little hard for me to help as I do not know your "thinking process." Also I am not sure if by calculation you mean visualizing the pieces, or on the other hand, how to efficiently look for the correct move on the board. I will thus tell you a little about both.
First on visualizing the pieces to think ahead I suggest you and two buddys practice playing blindfold chess (2 players playing at 1 time while the 3rd person makes sure the game is legit). Also for visualizing the pieces I suggest you solve some tactical puzzles and look over the games in chess magazines without a board. Of course being able to play a full game blindfold will take a LOT of practice but try not to do it more than 30 minutes a day or else your head feels funny.
Second, assuming you can visualize the pieces moving, you now want to 'efficiently look for the correct move on the board.' This I actually can not tell you as a Grandmaster taught me about it in 2 private lessons and it costed $$$ plus its kind of a secret : (. But I do suggest you practice looking for correct moves by playing lots of training games with time control of at least 15 minutes per player.
For more on improving your game you may want to see what I originally said in http://www.chess.com/forum/view/general/power-leveling
I'm having trouble caluating in chess, how do I improve upon this? Any books out there?