Re: How do I stop thinking?
Meditation as previously mentioned.
It trains your mind to adhere more to the will of your central executive, meaning you're more able to focus on what you're doing or what you want to be thinking about, or even think about nothing at all.
Try to know yourself. If you experience anxiety, try to know what causes it. If you have depressive thoughts, try to understand what causes them too.
Identify what thoughts are divergent in nature. What I mean by that is, what thoughts lead to more thoughts? Which ones have a finishing point? A common practice in meditation is focusing on the moment that your breathing inward becomes breathing outward. It takes your attention, but doesn't allow you to go anywhere from there. I use divergent thoughts to give me the pep to get out of bed, and closed ones to get myself back into bed.
I don't recommend alcohol, it can prevent development in the brain. Using it for medicinal purposes also encourages a habit-forming approach, which could be disastrous for your growth. You seem quite clever, it'd be a shame to waste such a brain.
Personally I listen to music. It filters out all the things that would take my attention from what I want to be thinking about. Mostly instrumental or heavy metal, where you can't understand the words which are also a source of distraction.