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• Save books as a single file rather than separate ones for each chapter / section.
• Add a table of contents if required.
• Check front matter, such as title page, copyright information and dedication.
• If your book has an index make each entry link to the appropriate point within the text, rather than simply listing a page number. Ebook content simply reflows to fit the display size, so page references are meaningless. For example, in Microsoft Word you can add a bookmark to an appropriate word or phrase within the text, then link its matching index entry to this bookmark.

Images

• Do you have permission to use all images? This is extremely important. Unless you took your own photographs or created artwork, it's likely the images belong to someone else and require a license for reproduction. If you use images without permission you could be sued for copyright infringement.
• Low resolution images will not provide enough detail, so make sure your source files are a reasonable size. It's best to work with large image files, saving smaller edited versions for production use. For example, using a 1800px by 2400px photo to create a 600px by 800px version. (Resolution is even more important if your images are also intended for print use.)
• Have images been saved in the appropriate file format? For example, the JPEG format is suited to photos but not images such as charts or logos. The GIF or PNG format is better for these. Also, images such as logos are likely to have been created as vector graphics in an application such as Illustrator, in which case we should be working with the original files for the highest quality.

Every project has its own requirements so get in touch if you have any questions. The Kindle Publishing guide may be useful if you plan to sell your book through Amazon.