A few pointers, for the independent author, about marketing, distribution, and legal deposits.
Marketing: Clearly, you want to sell as many copies of your own book as you can, but once the initial self-publishing honeymoon period wears off, as it invariably does, book sales will slump unless you are proactive in keeping your title in the forefront. Online, there are all of the social media platforms available to you: Twitter, Facebook, and the like. You could set up a blog, or a website (just one page) to promote your book, but static pages can become overlooked. In the real world, it is worth a visit to your nearest independent bookshop – perhaps offer a book signing – as most are keen to promote local authors. If you are a member of, or know, a local writing group, ask to give a talk and take copies of your book to sell. Send a copy to your local news office, or a magazine editor, for a review, as an inclusion in those publications will reach a wider audience. Some authors set up stalls at local fetes... There are many marketing opportunities available for an author willing to do the research and make the effort.
Distribution: Because self-publishing providers generally offer a print-on-demand (POD) service, where a book is printed at the time of sale, there is no wholesale stock kept, but the author is entitled to order copies of their book at a discounted price. It's worth ordering a dozen or so copies to sell privately. If you assigned a UK ISBN, it's also worth keeping some back in the event of a request from a book shop. It does happen! (If it does, enjoy the kudos of the moment, rather than envisaging long-term fame and fortune). Once your book is established online, you may notice it crops up for sale on websites, such as eBay, sold by a complete stranger for a high price. Do not be overly alarmed. There's little you can do about it, and in the (unlikely) event that someone purchases a copy this way, the seller still has to order the book from the retailer at cost, for which you will receive a royalty.
Legal Deposits: UK publishers need to give a copy of every publication they produce to the British Library. This system is called legal deposit and it's been a part of English law since 1662. It's done to maintain a central collection of publications that are preserved for the use of future generations, and to make them available from libraries. As a self-publisher, using a UK ISBN, you must do the same. You need to send one copy of every print publication you produce, within one month of its publication. You also need to deposit digital content, such as e-books. Other legal deposit libraries may also request copies from you. For more information, see the British Library's website page on legal deposits.
What happens next? Enjoy the financial fruits of your labours; however small they may be. Start writing your next novel!