In the list of things I wish I had learnt earlier, Mindfulness beats the rest by a wide margin.
Mindfulness is not just 'meditation'; it is certainly not closing your eyes and breathing for 'show', although that's how it begins.
It is a way of life, with two important insights that are realized over and over again:
(a) temporary nature of everything - including physical phenomena, and one's own thoughts, moods and emotions; applies in many different time scales from milliseconds to decades
(b) only thing that's real is the present moment; everything else is just thought; this leads to a better acceptance of past, deeper gratitude for the present, and an aspiration and planning for the future.
Although one needs dedicated practice (hence the closing of eyes and focusing on breathing) to begin to develop this 'muscle memory', the vast majority of the skill is built over a life-time - understanding the above two lessons and integrating them into thoughts and behavior again and again. There will be setbacks despite the best intentions (e.g., a bad moment, bad day or a bad year), but the key is recognize those moments and 'begin again'.
By far the best resource for this process is: https://www.youtube.com/@WakingUpApp. Takes only minutes to start. If you can not afford the subscription, they are kind enough to gift it to you for an year based on your request. I am a life-time subscriber and a fan.