inside cleaning..I read last year that the cpu has to be clean and thermal paste has to be clean and replace..plus vents,from inside out.
Unless is out of warranty or you know what you are doing you probably Shouldn't be replacing thermal paste on a laptop as you would probably void it....
With a desktop pc its a different story, you will find it easier as desktops are meant to be user accessible to a good degree.
Can having a laptop on your lap too long cause it to overheat?
I had this problem... mostly because the intake vents are on the bottom and the outward one is on the side. And this is when I tried to run Oblivion on the poor thing (integrated video cards aren't fun at all). I either use a wooden board or a nice plastic minidesk that sits on top of my lap now and don't have problems with it. Mostly depends on the type of work you're doing.