Moving your focus from thoughts to actions for a more fulfilling life
A thought (or rather, the thinking process itself) is a great tool when it's used for the right purpose (such as working out a strategy or vision) but could be a nightmare when let loose to wander on its own (worrying about future events or uncertainty, regretting the past events, etc.). Unfortunately, it's way too easy to lose focus and delve on the second kind of thoughts rather than the first.
Due to the way our minds are structured (or perhaps life itself!), it's effortless to get astray but takes a lot of deliberation and effort to get back on the right path as far as thinking process is concerned. Delving into the past or worrying about the future can become a kind of addiction sometimes (though "mental or cognitive loop" might be the right term) resulting in depression or other mental illnesses. The only way of coming out of these loops is to become more aware of them and reminding yourself that the action you take right now (in this moment) is the only way you can affect the outcomes or change anything in life.
Consequently, it seems as though having any kind of thoughts at all is counterproductive (unless in those rare cases where they're used to devise a strategy or vision). But thoughts are like those fluids that just keep coming out of that gigantic spring called mind whether we want them or not. How nice would it be if only the positive or useful kind of thoughts (strategy, vision, etc.) came from this spring and not all the crap? But for that, we must learn to not get "affected" by the wrong kind of thoughts first. In other words, we must not focus on them and just let them be.
Once the mind learns that we are no longer affected by these thoughts, it stops sprouting them (just like a media house would stop telecasting a TV show or newspaper would stop printing once it realizes that the audience is no longer interested!). Now, how do we go about the business of not getting affected by the thoughts? Perhaps the only known way of doing this is through Meditation. And a particularly effective form of such meditation is Mindfulness Meditation. Learn about it, read about it and most importantly, practice it if you're serious about letting those unwanted spring waters stop!
Mind is a good servant but a bad master (Vedanta Proverb)
Happy Self Improvement!