There are things about my past that I regret. I think we're all lying to ourselves if we say there is nothing we wish we could have changed. Yes, we grow and learn from those mistakes, but some lessons we don't want to learn the hard way. After many years of messing up, moving on, and repeating, I've come to the conclusion that there are a few things in life that everybody should keep in the back of their mind, regardless of regrets, mistakes, and lessons learned the hard way.
1. Wait to form a reaction. I say a lot that "anger is a wasted emotion unless used to make a difference", but if that difference is to rip apart someone who ate your leftover Chinese food, it's not worth it. Wait a 24 hours. If in 24 hours you are still mad about something that happened, then respond. But only after 24 hours of mulling it over.
2. You should care what others think of you, but only if those cares will lead to self-improvement rather than self-destruction. We, as people, should always be striving to be a better version of ourselves and that can never be achieved if you truly do not care what others think of you.
3. If you have nothing nice to say, don't say anything at all. (I just cringed writing such a cliche.) But it's true. If what you're putting into this world will do nothing but tear someone down or fuel a fire, bite your tongue and move on. The world has enough negativity in it as it is.
4. Stop feeling sorry for yourself. This one is said a lot too. You work hard every week to bring home a nice paycheck - buy yourself something nice. You eat healthy as often as possible in order to be healthy, so a piece of cheesecake won't do you any harm (and chocolate is good for you in moderation, so eat some!). You wear yourself out from various daily activities, so take a break and have a movie marathon and be lazy for a day or two.
5. "No" is not a bad word. I shouldn't need to explain this. Respect yourself enough to say "no" every once in a while.
6. It really is a good day for a good day. I used to hate it when people said that I determine my own happiness, as if I could control the things life throws at me or the emotions I feel. But when it comes down to it, you are the only one who can say "you know what, this will pass. I will be okay." And that is just what you need to do - acknowledge that you will be okay, and you will have a good day, because, you know what? You deserve it.