Test the EPUB in Adobe Digital Editions, Calibre, Nook, and any other Ereader but go back to the MS Word document to make changes
Tip 5: Immediately after EPUB conversion, test the EPUB in Adobe Digital Editions, Calibre, Nook, and any other available Ereader. Make note of the errors and go back to the MS Word document to make as many changes there as possible. Then re-upload the doc and make a new EPUB. Do this several times until you can no longer fix errors. At this step it is much easier to make changes in the MS Word document than in the EPUB. Although not all format errors can be fixed in this step, it will certainly save valuable time. Make careful notes of what you cannot fix before moving on.
– Greg Lundberg, Quicksilver Books, “How To Publish An Ebook For Under $350,” March 2012.