Some people do it via Facebook Ads or something. I don't really reply on promotions for gigs.
The delivery speed, good communication and of course, high quality delivery can bring in more and more visits and orders.
A good alternative is create new gigs based on your most popular gig - so you can introduce the new customers to another gig (if they need a dfifferent service) in this way, it grows your all gigs in a more natural way rather than driving everything with cashes.
Good luck!! : -D