I've started uploading the books I've written to Kindle Direct Publishing.
How can I promote them, on a shoe-string budget?
You might find this post useful.
From the link:
In this article, you will gain: An understanding of how these book promotion websites work A list of the best book promotion websites, free and premium A couple of options in order to not have to do this yourself
Best of luck! Promotion is exciting and challenging.
There are so many different strategies you could use from social media to blog hops to promotional sites, but there is no quick and simple answer as to which would work best for you. I would suggest joining a writer's forum where other writers discuss the strategies they have used and provide feedback on what has or hasn't worked. One that I use and have recommended frequently is the Kindle Boards Writer's Cafe. You will find dozens of discussions there on different strategies, and you can decide for yourself which ones to try.