Recognize it. Identify the situation which creates the negative thought. We all have those times (or places, or people) that ignite feelings of negativity, frustration, and worse. Sometimes we fully anticipate it, and other times they seemingly come out of nowhere. The key, and the best start to gaining control of your thoughts, is identifying and recognizing the situation as a trigger for these emotions. Admitting that it’s an issue and acknowledging your tendency towards this negativity can be hard (pride and whatnot), but it’s important. It helps you identify where you may lack control. Because if you don’t know the ways in which your thoughts control you, it’s nearly impossible to change the narrative and take back that control.
Find it. Trace the feeling back to the initial and/or recurring thought. All emotions stem from thoughts. Sometimes they are so rehearsed and repeated that they don’t even feel like conscious thoughts, but more like an automatic reaction. But if you can get to the bottom of what the thought is, you can help uncover the reason for that emotion. Furthermore, you can start to breakdown the validity of that thought/emotion altogether.
Challenge it. Once you have your initial thought identified, challenge yourself to not accept it as fact. Keep in mind that this is a thought that you’ve chosen over and over, but that doesn’t make it the hard truth. Are there any other perspectives to consider? Is the thought 100% true? Does this thought NEED to be one that you choose or are you just in the habit of thinking it?
Change it. The act of changing a negative thought is tricky. It’s often assumed that this means turn the negative thought into a positive one (example: “I’m terrible at public speaking” becomes: “I’m AMAZING at public speaking!”). That’s not helpful. It’s not helpful because you know when you’re lying to yourself! So you don’t believe this new “positive” thought, so it doesn’t change anything, so you continue your resentment towards public speaking (or whatever situation you’ve identified in step 1). The replacement thought must be helpful, and also true. This could look like: “I’m terrible at public speaking” becomes: “I’m prepared for this speech”, or “this could be my best speech yet” - both of which would be a HUGE improvement upon the old thought. See?
Practice it. Once you’ve gone through steps 1-4, you can’t expect an automatic shift in these thoughts/reactions. Consider how long you’ve been drilling those initially negative thoughts into your head! That takes a lot to undo. So, practice. Do it again and again and again, with the goal being: give more power to the helpful thoughts than to the unhelpful/negative ones.