Cheap, safe and effective:
• Take sheet of Bounty paper towel off roll
• Wet completely with lukewarm water--nothing else
• Squeeze out thoroughly until no more water drips out
• Examine screen and blow off any grit if present
• Open damp paper towel and use to gently wipe screen
• Let air dry
• After cleaning screen, use the damp paper towel to gently wipe down keyboard, wristrests and trackpad.
Other advice:
• Keep a sheet of plain white printer paper between keyboard and screen when closed to prevent transfer of anything from keyboard
• Don't eat or drink while using your laptop
I have been doing this for years: through PowerBook 180, PowerBook 1400c, Pismo and now PB G4 12 1.33. My screens have always stayed in mint condition.
Enjoy