As you build your set list, rehearse, and play your gigs, do so with the conscious intention of building and maintaining your fan base. Make the commitment to keep people informed of your doings at every step. Create opportunities for your supporters and potential clients to interact with you. Plan small and intentional acts of gratitude; respond when they make contact, and follow up on any leads they give you. Carry your cards or publicity materials everywhere you go. (Musicians always have a few bumper stickers in their cases and backpacks. Always.) Be available to people; answer e-mails and messages. If you really want to make an impression, send the occasional handwritten thank you note.
Whatever strategy your band creates to maintain communication with your fans, make sure it is a conscious strategy. Be consistent about it. Listen to your fans and make alterations as necessary. Never let it fall by the wayside.