Use social media to amplify word of mouth: reviews, post photos of gigs, get active in communities.
Also use search. SEO and PPC/Adwords. Plus have a website that is smick and converts well. I work in marketing (part time, DJ business is too busy) and run a mobile DJ business. But SolDios is right the best way to get gigs is word of mouth. Due to my marketing efforts I get tonnes of inquiries from people who find from search who really have no idea who I am. Out of these inquiries one in 10 book because they are looking for a cheaper price usually. Out of the word of mouth inquiries 90% book.