The brain can be thought of as similar to a muscle in that the phrase 'use it or lose it' also applies.
The more you use your brain i.e. by reading challenging books and reaching to understand them the more connections will be formed in your brain between neurons. Therefore your brain will become more efficient and intelligent.
There are many memory techniques that you can find on the web that wil DRASTICALLY improve how easily you store things you have read or things that people say to you.
Also eating right and taking fish oil and vitamins will definately help.
Drink lots of water throughout the day.