Give 'em away.
Seriously. You have to be ready to give away fully half of your first print run as promos. This is an investment in your career - send them to every magazine, radio station, and (in the case of hip hop) DJ who you think might play or review it. Make sure you have a good one-sheet - that is, biographical information and a brief but punchy description of the music (but be careful about photos - not sending a band photo is better than sending a crappy one, which most of them are).
There's no guarantees in any of this, of course, but the more of your music you get to people who have the power to tell other people about it, the better your chances are down the road.