I would also maybe add "picking a name that's impossible to Google and hard to remember".

The number of emails I get along the lines to "Your trial period of Foowazzle will expire soon" and my reaction is usually "I can't remember what the hell Foowazzle is".

In fact the reason I often fail to actually use trials of potentially interesting services after signing up is because I forget what they are called and can't find them when I need them.

At least "Foowazzle" would be easy to search for...