It's often referred to as mindfulness, and it falls under cognitive behavioral therapy. I've had trouble finding useful links, so I'll repeat the practical info I was taught.

Pretend your active focus or attention is like a fishing line. Pick a single thing, usually a physical object like a tree, and "cast" your focus onto that. Focus on specific parts of the tree, the bark, leaves, how the wind moves through it, how it makes you feel, etc. This will cause your attention to wander. Being aware that this is happening is crucial. "Reel" your attention back in and focus on just the tree again. Repeat this for roughly 15 minutes, at least once per day. If you can only manage 5 minutes at first, that's still a great start.

You are effectively training your brain to be aware of it's own attention. The idea is not to prevent wandering or emotions, but to be mindful of how those thoughts got there, and what you are thinking and feeling. In essence, how could you possibly control your thoughts if you aren't even aware of them?

Your zombie comment was something I was worried about at first. Spoiler: you're still free to act on those emotions or thoughts, but now with undivided attention!