I believe his style is a mixture of Parisian, Rockstar, and Bohemian elements.
Buy yourself a pair of Ray Ban Wayfarers or any other pair of vintage looking sunglasses. I don't think I have seen him without a pair of glasses.
Buy a tough and rough leather jacket. This adds a tough, rebel feel to the whole look.
Dress in dark colors like black, charcoal, and dark brown. He tends to shy away from bold and bright colors.
Get a bunch of rings and leather bracelets. Have you noticed how many rings and bracelets Johnny Depp wears??? He wears a ton of them!
Buy a worn looking leather belt.
Wear dark, faded, and distressed jeans.
Buy dark or black muscle T-Shirts.
Buy some leather boots or shoes. They should also look worn.
Buy a dark colored fedora.
Grow a goatee and a mustache.
Get a tan.
Go to the gym and get in shape. Don't get too buff. He has muscles but he doesn't overdo it.
Act mysterious and rebellious.