Firstly cut off the top of the can and then cut the sides into strips (about 8). (EDIT: 12-16, if observant you'll have noticed that I did 12, following my own instructions I tried 8 next time, which didn't work so I ut them in half and 16 looks better than 12.)
Bend these out at the base and then fold across diagonally and tuck under each other. I forgot to take more pictures so I'll find a more helpful link. Here is the finished product:
I'm using mine as a dish for earrings, it could be used as an ashtray too I suppose.
Here is a wonderfully clear video/slideshow, which is probably a lot more helpful than my instructions.