If you are willing to spend money on it, then you can explore the option of Facebook/Twitter Adverts. There are also other advertising marketplaces which sell banner advert space.
Other unconventional methods involve shortening your Fiverr gig URL and putting it on your business card, email footer links and so on. If you are able to write a post that goes viral on Imgur/Reddit, that’ll bring in some sales.
It depends on what niche you are targeting. If you participate in niche forums and establish yourself as an authority in your niche, you will start seeing a steady stream of sales from your own forum signature link. If you are a programmer, there’s Stackexchange, Slashdot, if you are a designer, there’s Dribble. If you are a Youtuber then you can try getting a shoutout from any of the popular Youtubers like RomanAtwood.