I have followed the way what Fiverr actually recommends to promote Fiverr Gigs. Sharing gigs on social media is the most effective way as well like sharing on-
As we all already known that Facebook is the most popular and top rated social media, so you should promote your Gigs here to get more impression. Just share your Gig links to Facebook groups.
Successful Graphic designers use Twitter for Gig promotions. You can try it too. Find your target audience and research about hashtags, share links with pictures etc.
You can use pinterest for Gig promotions. If you don’t know how to use pinterest, then you can take some idea from google.
But you should maintain a standard quality to create Fiverr Gigs first. If you have quality, surely you can sell your Gigs. The quality of your product and price is also important, because buyers always prefer qualities. If you have standard quality Gigs with best product in a good price, you can BOOOOM!!