Once you get a new Ghost blog up and running you'll probably want to customize it a little, to stand out from the crowd. So here's a list to get people started, based on my own experience.
Get a new theme
On the Ghost marketplace you can already find lots of beautiful themes, both free and paid.
After you settle on one, the instalation is quite easy: you just need to upload it inside the content/themes directory. The only downside it's the fact you need to restart Ghost to see the new theme in the admin panel, but other than that, you're pretty much done.
There are more informations on the Ghost docs site regarding themes and their instalation, including info on how to make your own theme.
Set up your mail
Again, all you need to know it's already documented. There are many options for you to choose from, and info on how to do set it up.
I ended up using Gmail, since it seemed the fastest and easiest, taking a total of... 2-3 minutes?
One rather major thing Ghost is missing at this moment is the possibility of leaving a comment.
However, nothing stops you from adding a 3rd party solution, like Disqus or Facebook comments.
Changing the favicon
Last but not least, it's the favicon! The default one is not that great. Once you find a better one, there's a very helpful topic on Ghost's forum, covering up everything you need to know.