If you remove the glass panel with a suction cup, you can clean the inside and outside with an iphone or ipod microfiber cleaning cloth (thats what i use)
alternatively, you can use a dust/lint roller on the screen (apple has a kit for it, but its not cheap, or made to be bought for a once off use, here is the link)
The difficulty is making sure you dont leave finger prints or smudges on the underside of the screen. also, try and find as clean an environment as you can, as dust will always seem to settle in between the layers while you work on it. A tip is to tilt the display as far forward as possible, then dust falling straight down wont land straight on the LCD panel...
It typically will take a few on and offs to get it perfect, but having natural light from a window helps show up any smudges in the process.
have fun. :-)