You clould try to sell targeted traffic, infact I just published a blog post about the subject, you can read it on my Internet Marketing Blog, Its targeted towards SEOClerks, but it should be applicable to Fiverr as well It will also teach you how to write an effective sales pitch.
Whatever you decide to do - I would recommend over-delivering. This will help you get repeat business, as opposed to simply working hard for new business all the time. Also decide on a service where you can up-sell with complimentary services, and higher price-point "Gig-Extras", e.g. 1st: Provide an SEO Analysis, 2. Provide the needed Silver Package SEO Service, 3. Provide Gold Package SEO Service. Also create a "Tip" gig, with some cool writing that gives you some personality. So you and your clients can build long standing relationships. Some people do "Extra Gigs" tips also, e.g. Buy Me A Coffee, Buy Me a Burger etc. Best of luck!
You need something that is easily replicable so you can churn out 10, 20 or 30 a day. And have lots of upsells to get a higher revenue per customer. Depends what your skills are but backlinks, social media and general SEO reports are very popular and easy to scale too.
I would recommend you choose a service which is easy and cheap for you to deliver and that you can potentially sell large quantities of. Traffic is always quite a good option as are SEO, backlinks and social media followers. An alternative site you may wish to sign up to is SEOClerks.com.
Choose something that you are good at and deliver a good quality gig so you can always have people paying for your gig. Also I think you can always ask in the Fiverr forum for more information.
I Just got a Email From Fiverr the other day they now have 2 Million Gigs On there platform!! There is alot of competition on there but what you have to do is Live up to what you say and get good reviews. Other then that people will pick the Gigs with the most "Positive Reviews"! Try to come with a UNIQUE Gig! I hope this helps in your quest.
To put a slightly different spin on this. you could also look at what you can buy off fiverr and sell somewhere else for a profit. You can think way outside the box here. maybe taking artwork/cartoons and printing them on t-shirts or mugs or it could be as simple as bundling a couple of related gigs together and selling them as a package.
Best services that work on fiverr are logo designing. If you're good at it, you can earn pretty well. Another thing you can do is buy a software like Scrapebox and offer Bulk SEO Link Services. Be creative and you're surely earn on Fiverr.
It's hard to say without knowing your skills and background. Just put up a bunch of ads for services/products you can provide and from there you will likely figure out what works well for you.
With your gigs you want to be offering something better than the other people trying to sell the same thing. You want to go above and beyond with you gigs. Some gigs that sell well: 1. Video Testimonials 2.Ebook Design 3.Teach People How To Get Twitter Followers(make a video and when they buy your gig send them the video, Use the website Twiends.com) 4.Post A Tweet 5.Write Articles 6.Sell Ebooks 7.Voice Overs 8.Youtube Comments 9.Write Amazon Reviews 10.Send A Postcard Well I hope this helped.