It's like any other ninja skill, it gets easier as you practice. I keep failing. It requires constant effort for me.

Stoic pro tip: start by controlling your opinions (through rational thinking). It's a lot easier to do. Feelings are always a response to sensory input filtered though opinions. Example: "I shouldn't be treated this way, this is deeply unfair" -> "I can't control how people treat me, there is no *should* for things I can't control"

Read. Read lots of books. Never turn on the TV and if someone else has, try to block it out (very hard). The reading is not an instant mind change. But over time, you will 'gravitate' from passive engagement in everything to questioning everything (active engagement). Reading is very hard at first because the current education system in USA does not teach independent thought and exploration (but learning process and things). Over time, reading will change the type of books you want to read - re-enforcing the 'question everything' state of mind. TWO years later, enlightenment feels extremely good - almost an elevated state of mind as you listen to people talk in the background. May take 3+ years depending on how programed you have become. You will absolutely learn to control your feelings, and the emotions that drive them - because you will understand where it comes from. As a side note, you will also become VERY heathy (eating the right foods and engaging in healthy activity)!