always, always, always throw a towel, old t-shirt or something over the tank when working on yer bike. make it part of the ritual of assembling parts, tools, beers, etc. it's a lesson learned one way or another. I learned mine on a dirt bike years ago but fortunately didn't care too much as the thing got beat to hell anyway.
Being a clutz, I learned a long time ago to through something thickly soft on there. Somewhere along the path I found a really nice old-fashioned quilted furniture pad. Also, if it's going to be something involved, I've found it's easier to remove the tank and get it out of harm's way. Makes access to a lot of things easier as well.