I am a relative beginner to Twitter. I do not give a hoot what Kim Kardashian is having for her breakfast and cannot name the chaps in One Direction. It is also my experience that this is the same for my clients (who are often newbies to Twitter too).
What I do use Twitter for is to follow other people who are interested in B2B content marketing and all I tweet about is B2B content marketing. This is central to what I need to know about to do my job and I have found it helps having a focus. I have tried to be pretty choosy when following people and certainly do not just follow someone because they retweeted something I wrote about.
With my clients who do tweet personally as well as for work I suggest they have two accounts. This seems logical to me. It means you can talk about Arsenal and moan about your kids with one audience whilst still developing your professional twittersphere.
I am sure I have heaps to learn about the best way to use Twitter but kicking off with a focus has certainly been a good way to start.
What Should You Tweet? It depends on what you want to get out of Twitter. If you just want to read the news then really there's no reason for you to tweet anything-- seriously! If you are trying to get followers then you should think about focusing your tweets thematically on certain topics. If you follow me, for example, you will get a smattering of politics, social media, Nationals, and UVA news. About 50% of my tweets are simply retweets from my feed. Sometimes I do this simply so that I can go back and look at the article later, but often it is simply something I like or find funny and think that my followers will as well. Retweeting someone can also get them to follow you.