This is one of the brain tools I can't really understand anymore how I managed to do without.
My favorite - and largely only - form of meditation that I practice regularly is mindfulness mediation. I first encountered the concept about 15 years ago when I came across a book called "Wherever you go, there you are" by Jon Kabat Zinn. I was about to become a PhD student at the time and so my natural instinct was to think that this was likely some trivial nonsense. But I was in enough adolescence-related mental pain at the time that I thought I'd give it a try. It changed the way I looked at myself, and at how the mind works. It was the first time when I fully realized, I am not my thoughts, and that thoughts are objects I can study objectively. I've been expanding on this concept for quite some time ever since then.
I most recently came back to regular practice with the Waking Up app, which I very much like (and I can also recommend the book with the same name by the same author, Sam Harris).
Mindfulness meditation has become a key tool for me, and today, as we are in the midst of the attention economy, being able to realize when someone tries to hijack your mind has become extremely valuable. That's of course in addition to all the benefits you get from realizing when your mind gets hijacked by your own thoughts. I now rank the ability to do basic mindful mediation so highly that I will teach my kids to understand it before I teach them how to code (and if you've ever been on the receiving end of one of my sermons about everyone having to learn how to code, you know what that means).
So this is my first advice: Look into mindfulness meditation.