Picture by chaparral
Lifehacker reader Rhett wrote in with this advice:
Don't ask me how I found this out, but if you've got crap on your iPhone screen that won't come off with a tissue, giving your iPhone a good lick or two and then giving it another go with a tissue is a win every time.
We take no responsibility for your phone if you try this out. Another useful iPhone cleaning tactic is using a paintbrush to get gunk out of the speakers. Thanks Rhett!