How do you stop being a slave to your unwanted thoughts?

I don't know if u can relate, but if you are somebody with anxiety, and you think a lot, and habitually those thoughts become very negative, and you start to believe these thoughts, and fear them, how do you stop this habit ? how do you stop being a slave to unwanted fearful thoughts, that for example. you want to go do something you enjoy, but you have a fearful thought about doing that, and then don't do it. Or a thought of something like' oh well last time you did that your anxiety was worse and your OCD was worse, so it's best not to do that ' ...even if its something you would like to do ? make sense?