Let’s clear up a misconception about platform and self-publishing. For the average first-time writer, self-publishing is not a reliable way to expand your platform. It’s simply a way to publish on your own, without the help of an agent or the resources of a traditional publishing house. Agents do not see self-published authors as any more serious about finding an agent than non-self-published writers.
Authors with well-established platforms have better odds of self-publishing lucratively and successfully, but it’s important to have a realistic mindset about where you want to go from there. It’s a full-time job to sell books without the backing of a publisher. Selling (not giving away for free) fewer than 10,000 books and/or e-books can demonstrate that your project lacks strong audience appeal. If you then try shopping that self-published book to agents or publishers, they’re likely to view it as “sloppy seconds.” Self-publishing is not a precursor to publishing for writers hoping to secure agent representation. It is the real thing. Once a book or e-book is published and given an ISBN (an industry tracking number), it has a traceable sales history. If your book sales are not a selling point, your work, not the medium used to publish it, will be seen as the cause. Self-publishing can benefit some writers, but if you choose this route make sure you are OK with the possibility that that project very well may not be traditionally published later.
The good news is that even if you have already self-published and those sales were not brag-worthy, most agents will not be deterred from considering submissions for your new, unpublished projects. Just make sure you are transparent about your self-publishing history (without overemphasizing it) and that the new project isn’t intended to piggyback on the self-published work in any way.