Add your name, location, and website. Under your profile picture, you have the choice to enter your full name. Adding a full name allows you to keep a professional aspect regardless of your username. You can also enter a location to let people know where you're tweeting from and link to your homepage or blog if you desire.
Work on your pithy 'bio'. Make it eye-catching and interesting. Do it just right and it will help you build up followers; people thinking of following you do read the biographies to see if they have reason to follow you. Bear in mind that a biography can be up to 160 characters long, so you'll have to keep it short and to the point. Don't worry about typing your real name or website URL here—those can both be entered separately (as shown in the previous step).
Decide whether you want your tweets to be posted to Facebook. This can give you more view per tweet. If you so desire, click the "Posts your Tweets to Facebook" button at the bottom of the profile page.
Edit your language and time zone. Under the "Account" tab of settings, you have the ability change the language and time zone that your Twitter is in. Do so by selecting the desired language and time zone from the drop down menus. You can also change your username and email address here if you ever need to.
Check the box below time zone to add a location to each of your Tweets. This is different than the location on your profile—it is specific to each tweet and can be as general as a town or as specific as your exact location. Even when this feature is enabled, you have the option to turn it on or off with each individual tweet.