Know WHY you're reading: are you reading for entertainment or to learn something? Decide why you're reading before you start and you'll greatly improve your comprehension and your enjoyment.
Scan before you read: look at the table of contents, index, topic headers, photo captions, etc.
Environment: read in an environment that's comfortable for you.
Focus: remember, you're reading with a purpose, so focus on that purpose and the material. If you lose interest or keep losing your place, take a break.
Practice: the more you read, the better reader you'll become (and smarter, too)! So, feed your mind: read!