I guess I actually have two pieces of advice for you. Both are things I've learnt through personal experience and both are things I live by daily.
The first, 'take everyday as it comes'. It's probably something most of you already do but if you're like me, a planner and a worrier, then this is something you need to try and live by. I am the worst, I plan everything months ahead of time and even though this is great as being organised is very helpful for day to day life, I worry over the tiniest thing not going the way it should. Since sticking to (or trying at least) this little rule of mine, I seem to be much more levelheaded and not so 'spontaneous' in my thoughts. It also stops me from worrying when something goes wrong as instead of thinking of how bad it'll affect the upcoming weeks or how people see me, I just let it ride and take it all one day at a time :)
The second, and this is something I love so much, is something a friend said to me (who was/still is incarcerated). She said to me 'Never a regret, always a lesson'. she said someone had said this to her when she arrived in prison and it's something that she says to herself daily. And now, so do I. As you all know, I've had some bad experiences, bad ex's, bad 'friends' etc and whenever I start to think 'what if', I always remember that piece of advice I was given.
If I regretted and could undo all the bad things that have happened in my life, I would not be the person I am today. I wouldn't have the family or friends that I have and god knows what I'd be doing. I think it's very, very important to never regret a single thing you do, no matter how stupid they may be. And never regret a person you've met, no matter how bad they made you feel or how hard they made you cry as all of these experiences teach you not to make said foolish mistakes again :)
Hopefully, some of you can take away this advice and use it for yourselves. It would be great if it became as useful to you as it has for me. Thanks again @missy and @rambo for another great topic, and one where I get to be the responsible adult haha.