One of the things that you learn as an indie writer is the things that you should have pre-assembled before you start uploading your ebook to an online retailer (such as Amazon or Smashwords). My current list runs as follows:
Properly formated file (ex. a .doc for Smashwords) with all your front and back matter, plus a table of contents.
The front matter needs to include what edition it is (Amazon or Smashwords, etc.), the year of the copyright, a link to your Amazon author page (for the Amazon version) or Smashwords author profile (for the Smashwords version) or other such page, plus your social pressure "please respect the work of the author; do not pirate; buy your own copy" boiler plate. Try to keep your front matter as small as possible--it chews up space in the sample version, and you want people to read as much of your story or information piece as you can in hopes of hooking them into your ebook, and hopefully hooked well enough that they buy a copy. While you often have no control of the size of the sample, you can control the size of your front matter (if you can move something to the back matter, then do so).
The back matter is your bio and any ad copy and links you want to toss in for your other works. It also includes any sample chapters of your other works that you want to include.
Ad copy and keywords
You should spend some time before your upload day writing out your ad copy, so that you can copy and paste it into the relevant field when you are uploading. For Smashwords, you need both a short and a long description (400 characters is the limit of the short description--4000 characters for the long description). Resist the idea that you will be able to crank out perfect ad copy at the drop of a hat.
Your keywords (phrases) are words that one would use to search for your ebook that do not show up in the title or description. My most used keywords are "Golden Dawn" and "witchcraft" and "pagan"--"wicca" and "wiccan" tend to be included in my descriptions.
What category would you expect to find your ebook in? Where are similar ebooks?
Make sure that your title and name on the cover matches the information in your front matter. If possible, make sure that your cover looks good both at regular size and in the thumbnail version.
How much are you charging?
A snack and a drink
Because you do not want your blood sugar to tank midway though the process if things go sideways.
Enough time and energy
Besides these things, you need to allot a couple of hours to the upload process. Even after you do it the first time, you can be surprised when you upload as retailers make changes in their upload layout and requirements. Hopefully, you will not need it, but it is better to schedule plenty of time just to be on the safe side.
And do it on a day when you have plenty of energy. Nothing screws up the process like being tired.