A good way to get start using twitter is to look at your own email list and find anyone that that you already deal with that’s using twitter.  Friends, Family, workmates etc.  BUT WAIT !!! Read the following very carefully:

If your using twitter for yourself to tweet your mates or find out what all the hype is about then by all means choose a username that represents you or what your know as (or make up something crazy).

If you using going to use it for business, to represent your brand then you need to think carefully about the sort of username you use.  It is extremely important to have a Twitter profile that makes people notice your brand.

Think of your Twitter username and Profile as your first Advertising Campaign.  An effective Twitter profile will make potential clients follow you rather than just pass you by.  The initial overall impression that you make with your profile has to be BANG!!! … follow me.
Use your domain name as your username ahead of your brand or products.