The memory book by harry lorayne. Yes it's old, but it's really worth checking.

How to remember anything by Dean Vaughn is also good. Check this out if you have time.

The silva mind control method. They have good visualization information.

Note:

You don't have to buy these books, but if you can borrow a copy and read it. It may help improve your art.

A nice book on comprehension is written by john butterworth. This one is a very good book on reading.

Practice.