Keep it turned off!!! ;-)
No seriously, Laptops are notoriously bad when it comes to overheating. If you think that you've basically got a desktop computer (that quite often has alot of case space around it) crammed into a little laptop case, it's a wonder they don't catch light!
You will find lots of stories about laptops burning peoples legs when they sit with it on their lap and all sorts, but there is very little you can do.
I'd suggest having a look at any vents around the side of the computer - there may be a build up of dust there (the enemy of good cooling) try getting a vaccum on it and seeing if that'll do anything. Beyond that, if it's an older laptop, it might be worth taking it to a computer specialist (little town shop, not the likes of PC World) who can pull it apart and give all the fans, etc a good clean up. This can quite drastically improve the efficiency of the cooling.
If it were a desktop computer, then you'd get loads of comments about buying a new case, or bigger fans, but you just can't do that with a laptop!
Hope this is of some help to you!