I would say look at his interests... maybe an album cover of his favorite band, a skateboarding, wakeboarding, snowboarding type cake if he's into any of that. I'm trying to think of things my brothers are interested in and it's always video games, various "boarding" sports, jet ski's and/or boats and music. my cousin likes dirtbikes and my other cousin plays drums in a band so maybe just think of things like that and go from there. And if all else fails and you're doing a sheet cake, look at Cakery's stuff, she has a ton of fairly general boy themed cakes. I love her cakes.