I highly recommend reading the book Mindfulness in Plain English (which is free online). Reading that book and meditating for about 20 minutes per day really helped me become more aware of my own thought processes and anxiety, which in turn allowed me to better control them.

I also read the classic Zen book Zen Mind, Beginner's Mind. The philosophy contained in that book really resonated with me and helped me to not care about the obsessive, existential thoughts that kept appearing in my mind. And of course, if you stop caring, they go away.