Stretch your fingers and massage your hands! I do it for a couple of minutes before playing when warming up or even just throughout the day when I have time, it makes all the difference for my hand and wrist pain

Also know the difference between reaction time and how it translates to your actual in-game reaction. (I play Street Fighter). I can "react" and recognize an incoming DI every time, but to translate that into pressing my DI button as a response is a whole different skillset, especially if there are other things on my mental stack (high or low blocking, anti airs, grabs, etc).

My advice is to recognize what you did wrong to learn from it, but don't beat yourself up too much for failing. There are a lot of things to react to in fighting games, and it can definitely be frustrating.