Professional Twitterers have to perform different functions depending on the client.
But in general, you will have to make your clients Twitter account successful.
You job is to send out tweets, build followers, follow people, build relationships, start conversations, etc.
And yes I know, all these thing you are doing now anyway, but being a pro is a whole new level.
Twitter was designed for people, so that the can post their updates, letting everyone know what they were up to in the past few day.
But when you are tweeting for someone, that may become more complicated.
Often you have to work for companies.
This means that you won't just tweet about actions, as you did with individuals like yourself, but your job is to ask people their opinions.
You will have to react fast to the complaints, giving away freebies, coupons, announcing product releases, etc.
That is a hard job, because you always have to be in touch with different departments in your company.
But tweeting for a celeb is a much more painful procedure.
As I said, Twitter was designed for the "original" person, so that they can share their opinions, whereabouts without having paparazzis on their tails.
But as we know celebrities are busy, they want to automate everything, or better yer, hire someone.
But can you not overstep the line, where something real private, must stay private? You need to find balance between interesting and personal and that is really hard.
Well, this is what professional Twitterers do.