New Module? Check Permissions!
One thing that consistently trips up both new and experienced developers when enabling a new module are "permissions". I can't tell you how many times I've enabled a new module then cursed my computer for a few minutes thinking that the module wasn't working properly - only to realize that I forgot to set some arcane permission on the admin/user/permissions page.
So, next time you download and enable that shiny new module, be sure to not only configure it using its settings page, but to check its permissions!