Word of mouth...
Get all my work that way
obviously depends what trade your in, get a few customers, do the job right, don't overcharge, and word soon spreads.
lots of my customers are people who have used me before, others have heard/seen the work i've done, get new customers up the pub etc.
for people starting out having sign writing on your vehicle is a good cheap way as you will pick up local trade, t-shirt printing is cheap as well, also printing your own leaflets and posting them in local area and putting on local shop windows/notice boards. for those looking to advertise on the net,