We all have them. Some are bad for us, like smoking for example. However we continue to do it. There are habits that perhaps not quite so noticeable, but still bad for us. A good example of this would be negative thoughts. Why not keep a pen and paper to hand and make note every time you have a negative thought. It might surprise you how often this is.
You might find these thoughts will decrease over time simply because you are marking down on a piece of paper. Why not give it a try?