Twitter does not give you many options to brand your profile and yet, when you look at different profiles, they all look different. The first area where you can make a positive first impression on your Twitter profile visitors is you bio. You can tell in 160 characters what you are all about. I usually advise my clients to stay concise and to the point. Try to put one keyword that you are optimizing for into the bio. Also, add something personal. This can be a great conversation starter and as you know social media is all about conversations.
The second area where you can make a good first impression is the Twitter background. If you Google “Twitter background,” you get a lot of search results. I like http://www.twitback.com. But you can use any background you like. In the background, you can put a picture of you (remember: professional) or a banner. Since you have the whole left side of Twitter to fill up, you can add a bit more information in there. Do not overdo it and stay professional. Have fun.