Before going out and building a dedicated web presence, make sure your desired username is available consistently across several of the major networks. You want to keep it aligned with your business or product name, as well as simple and short if possible.

Use a tool like nameckr or KnowEm to easily search a number of social networks at once to see what's available. This may play into your username decision if you have a choice.

Once you've settled on a username that works and is available across a few major platforms, you'll want to grab those properties. Additionally, you may also want to reserve the username on other important social media platforms that you'll eventually want to expand to and make use of (think YouTube, Foursquare etc.).