I usually do so after a couple of weeks of anyone not following me back. Since I follow back anyone that originally follows me, I feel they should do the same. Why should I read tweets from them if they are not reading mine. That is my philosophy on that. I know some have a program to automatically un-follow someone that does not follow them but I prefer to do it the old fashion way, I know it is more time consuming doing it this way but I like doing it by hand so I can look at once again what these people including have on their sites. As the list grows and hopefully yours does, you tend to forget what some of them are offering. Such as book cover designers. I will be in the market for them in a few months. Right now, I am going through each of my published books with a fine tooth comb with my fabulous editing team, then I will republish my books with new exciting covers. All those I self published, the others will have to wait until my contract runs out. Getting back to twitter, I don’t understand why or how some people have thousands of followers yet fllows only one to two. I guess their shit don’t stink? Talk back, I’m listening.