Some women have a natural ability to layer on the baubles effectively, but guys have to use some caution when it comes to shiny jewelry. A watch, a tasteful ring and maybe one other piece (sometimes) should be plenty. Necklaces and bracelets on men can easily be too much. If you're going for the gangster vibe a'la the New Jersey mafia, then by all means, pile on the gold chains. But if you're looking for something a bit more subtle, pare down the jewelry -- a lot.
And don't oversize your choices or go for too much sparkle, either. There's a fine line between elegant and gaudy. If you cross it, you'll be risking a "lounge lizard" vibe that even your mom won't find attractive.