Free listings on Amazon for KDP Select publishers like myself, whilst less effective than they used to be (more on that another time) are still a good way of getting your work out there when no-one knows who the hell you are. Like myself. 
But it’s ALSO a good idea to get your work submitted to the various sites that promote said free ebook listings (of any type, not just Kindle); they’ll not only put your work on their front pages (provided you meet their varying requirements, and that they like you) but often tweet the link to their thousands of followers too. There’s an immense market of people that only read free books on their Kindles; whilst, in the long run, you won’t make any money off them, a lot of them will give you the vital reviews you need to help you on your way. If you think about it, it’s quite a nice two-way relationship; because these people are happy to try out new authors, a lot of them are happy to post a review, more so, in many ways, than your paying customers, many of whom will think that they’ve paid you your money for the book, so they don’t owe you a review (they’re right, they don’t owe you anything…but it’s makes an author extremely grateful when they do.)
Anyway, something I discovered on my free-listing-promotional-insanity-day was the extremely useful Author Marketing Club. It has a load of free ebook ‘marketing tools’ – nothing new there – but best of all, it has a page where the best of the free ebook marketing link sites all in one place. Even better, the links on that page (the page the above link takes you to) all go directly to those sites’ book promotion submission pages. It saves a lot of time, and you can go through the whole list in an hour or two. 
It might only get you another 30 downloads, but hey, if those generate even one new review, that makes it worth it, right?
To learn more about MY books (Woo!) visit www.lukesmitherd.com where you can buy them for Kindle.