You must treat it like a business from the very beginning. Taking this standpoint makes the promotion end of things much clearer. Look around you at other businesses. Most, if not all, of the standard business promotions will work for a band. Probably the first thing every band does is fliers.
Fliers are cheap and they work.
While not quite as cheap as fliers to produce, they are just as effective and much more businesslike. People generally keep business cards, while they rarely keep fliers. If you have a computer and printer at home, you might want to look into printing cards yourself. Card stock is widely available at office supply stores and is inexpensive. While you're still thinking about fliers and business cards, don't overlook press releases.