Try to take a few notes while you're reading. Pick the most important points, such as names and places and write them down. This way you will have you notes to refer back to if you can't remember something.

After reading a chapter, try to take a moment to summarize what you just read. If you can't remember the main points, go back and skim the material again to refresh your memory.

If you have just read about a famous place, you may want to look at a map to find out exactly where this place is located. If you are reading about an historical event, you may want to do some additional research on the web and read some biographies on the people mentioned in the book.

These are just a couple of my tips. I look forward to reading yours.