A few pointers, for the self-published author, about marketing, distribution, and legal deposit.
Marketing: Clearly, you want to sell as many copies of your book as you can, but you need to remain proactive in keeping your title in the forefront of peoples' minds. Use social media marketing to advertise your book online. You could set up a blog, or a website (just one page is fine). Arrange a book signing at your local independent bookshop; most are keen to promote local authors. If you know a local writing group, ask to give a talk – don't forget to take copies of your book to sell at a discounted price! Send a copy to your local newspaper and/or relevant magazine, for a review, as inclusion in those publications will reach a wider audience. Some authors set up stalls at local fetes... There are many marketing opportunities available to promote your book.
Distribution: Self-publishing providers generally offer a print-on-demand (POD) service: when a book is ordered, it is printed. There is no wholesale stock kept, but author copies can be purchased at a discounted price, so it's worth ordering a stockpile for yourself to sell privately. Keep some aside, in the event of a request from a book shop. It can happen! (If it does, enjoy the kudos of the moment, rather than envisaging long-term fame and fortune!). You may notice your book crops up for sale on e-commerce websites, at a high price. Don't be alarmed. There's little you can do about it (view it as free publicity) and besides, in the 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 Deposit: UK publishers need to give a copy of every publication they produce (both physical and digital) to the British Library, whether it has been assigned an ISBN or not. (A publication is defined as any work that is issued to the public – which a self-published novel for sale would be). 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, and to make them available from libraries. You need to send one copy of every publication you produce, within one month of publication. Other legal deposit libraries may also request copies from you. For more information, see the British Library's website page on legal deposit and on how to deposit your print publications.
What happens next? Enjoy the financial fruits of your labours; however small they may be. Start writing your next novel!