As a way to promote activity and stay in front of prospective customers, I use Constant Contact. http://www.constantcontact.com/index.jsp
You can add a sign up link to your web site and use email to regularly 'touch base' with your past customers and prospects. I try to do a monthly to bi-weekly mail blast in a news note format. Specials, successful events, menu ideas are all of interest to new prospects as well as past clients who may hire you again.
Some other things you can do for exposure require work output, and effort, but it's also a chance to 'practice' and get the quality of your food out there.
When I first started my personal chef service, I donated gift certificates to a couple of local groups to use as auction items. The scope of the gift was totally in my control, so I was able to limit my cost. By 'giving away' $300 of retail labor value, my donation became a 'high end' and 'high dollar value' item in the auctions. As such, my gift certificates became marquee items in the auctions, so my company name was splattered all over every flier and ad for each of the auctions. My actual out of pocket cost ended up being only the cost of food at less than $100 for each certificate. Trust me, I got WELL over $200 worth of advertising out of those two gifts. Oh, and as both were gifts to charitable organizations, I was able to write off the cost as a donations.
The other thing you can do is partner up with a local sports league or team. Little League, AYSO, Pop Warner, and most High School teams almost all have some sort of snack bar type set up for their games. Most of the time these are big money makers for the leagues and/or schools. Yet, for the most part, at least in my area, the menus are VERY limited. (nachos, burgers, dogs and not much more) I've approached a few leagues and offered to cook up some quality Q to offer a more premium menu at a slightly higher price to the customer. The by my donating the 'labor factor' of the BBQ the actual food cost of this 'high end' menu ends up being pretty much the same as, or even less than, the burgers and dogs. Yet, by charging an extra dollar or three, the league makes far more money. (Yes, I set the menu prices with future full pay BBQ business in mind. No point in under cutting the market, or slitting my throat before I even get that part of my business up and running!) We do this on a very limited basis for each event. Pork, and/or Tri-tip are options and when it's gone, it's gone. I intentionally undercut by a small fraction what I expect we may need for a game. That way we never have left overs, and it creates urgency with those who ‘miss out’ to buy early at the next game.
The league, or team, covers the cost of food; I ‘donate’ my labor. The deal I make is that I get to advertise my service via cards, banners, flyers etc. at the games in consideration for my food prep and labor. The high schools generally even offer to mention my company name over the PA as part of their appeal to fans to support the school by buying at the snack bar. In addition to the advertising, I get access to the school kitchen facilities to prep food for the games, and they have NO problem with me prepping extra stuff in their state inspected facility while I’m there. (Read, free access to a commercial kitchen!) Again, in my estimation, I get back far more in business exposure and advertising than the time and labor costs me. And, that’s even before I factor in the value of the commercial kitchen access.
Ok, sorry this got so long winded. I hope the ideas help.