Nick Burrows wrote:What is the best way to improve tactical ability?
Aside from problem books (I am working through Polgars) does anyone have tips to improve on visualisation & calculation?
Are there any good books on this specific issue other than puzzle books?
Personally, I think the best way of improving your tactical ability (and subsequently visualisation and calculation) is by solving chess puzzles as you do already. However, I think it's important to take a structured approach (as has already suggested). Three books, which I find excellent, are Maxim Blokh's "The Art of Combination", "Combinative Motifs" and "600 combinations" (in total some 3,000 puzzles). They're all taken from real games - or composed to look like real games - organized along themes and generally goes from very easy to extremely difficult (some with solutions for both white and black), which means that you gradually build up a pattern recognition of each different theme. Another very important thing about Blokh's books is that they contain no hints, so you have to approach them without preconceptions.
Many strong players (GMs and IMs) advocate making training resemble real tournament situations as closely as possible. Therefore I would recommend you do something like this:
1) Take, say 5 or 6 puzzles.
2) Set a clock for the period of time you think you will require to solve them. In his books, Maxim Blokh has graded all puzzles by level of difficulty from 1 to 12, which makes it possible to set "score bands" for the puzzles you're solving (e.g. if the total of the 5 puzzles is less than 25 points, set the clock to 30min, 25-29 points to 45mins, 30-34 to 1h and so on).
3) Set up the first puzzle on the board and start the clock.
4) Try to figure out the solution,
without moving the pieces, and write it down.
5) Move on to the next puzzle until you have solved them all.
6) Check the solutions.
Try to solve all puzzle within the alloted time. This way you're working in a more focused manner because you're not only trying to solve each individual puzzles, but you're also competing against the clock - just like in a tournament situation.
In my view, this works better than only solving the puzzles by looking at diagrams in a book or on the computer screen, because, apart from the fact that it's more tournament like, as you set up the positions on the board you can also try to put the positions up as quickly as possible (that is, with as few looks at the diagrams as possible), in order to improve your cluster pattern recognition (of pawns and pieces).
And one final thing, as Jon pointed out earlier, this training has to be done regularly; every day or other two or three days to have any real impact.