1. Your fic
Start from an AO3 download: HTML or EPUB (optional)
Drop the .html or .epub file here, or
On AO3 that's Download, then HTML or EPUB, on your own work. EPUBs you saved before the outage work too. Title, tags, summary, notes and chapters fill in below, and you can still edit everything.
2. Your page
Upload the file to your site (on Neocities: Dashboard, then Upload) and it works as it is. No scripts, no outside files, one HTML file per work.
Readers asking for an epub? "Download .epub" makes a standard EPUB 3 book of the same work: a title page with your tags, one file per chapter, a table of contents. It passes the official W3C EPUBCheck, and e-readers such as Apple Books, Kobo and Calibre read EPUB 3.
3. Your shelf: many works at once (optional)
Moving a whole archive? Drop all your AO3 downloads (HTML or EPUB) here at once, or add the work you made above. You get one .zip with a masterlist page (index.html, grouped by fandom) and one page per work. Every work page links back to the masterlist. Theme, font, the "don't repost" line and the credit line follow your choices in step 1.
Drop several AO3 downloads here (HTML or EPUB, mixed is fine), or choose them:
Unzip it, then upload every file to the same folder on your site (Neocities: drag them all onto the Upload area at once). Your works are named after their titles; index.html is the list. If you upload to your site's top folder, the masterlist replaces your home page, so put the files in a folder like fic/ if you have a home page already.