On the Goodreads website, open My Books, then Import and export (or go straight to goodreads.com/review/import) and press Export library. Goodreads prepares a CSV file and gives you a link to download it.
Press Import your Goodreads library. Once you've signed up or signed in, Bookfern opens the import. Choose the file you downloaded.
Before anything is added, Bookfern shows how many books it found on each shelf. Books already in your library are skipped, so importing twice does no harm. Covers, descriptions and themes fill in over the next few minutes.
Every rating, note and book you put down tells Bookfern what you like. With your whole history imported, its first suggestions already know your taste, and each one names the books of yours it comes from.
See how suggestions work