How Do You Improve Calculation?

I'm not very good at it and want to improve but I don't really know how I'm supposed to do that. For example in this position I just played a bad move:

Tactics.

No, I mean tactics. Solve puzzles without moving pieces. That will help your raw calculation skills.

Learning to assess a position and coming up with candidate moves is another subject, but equally as important. You have to choose which method of analysis works for you, though. There's a few worth looking into. Many like Silman's imbalances.

Solve a whole puzzle to the end without moving any pieces. All in your head. Try to find the best defense for the opponent. Calculate at least two different defensive tries pretending the opponent sees everything too. The defensive moves should try to screw things up. Usually this means avoiding a recapture, ignoring a threat, playing a check, things like this.

After you've calculated the whole line and are satisfied with your solution, write it down (including any variations). Visualize the end position clearly and write how much material you're ahead at the end (all of this still without moving any pieces). Now check your solution against the puzzle solution. Did you find right idea? Did you find the best defensive moves for the losing side? Remember tactics are all about forcing moves. If the opponent can ignore a move, it's probably not the right move.

Do this for a few puzzles a day, every day for a few months and you'll notice a pretty big difference I think. Not only is it visualization practice, it gives you a heightened awareness of captures, checks, and undefended pieces.