I don't feel like I am in much of a position to give advice since I'm not doing that well, but at the same time, I do feel like I have learned a few things from experience that I would like to share.
One realization I've made over the years is that often times, you have to be ready to take an opportunity before it shows up. Also, the opposite - it won't do you any good to have an opportunity if you aren't ready to act on it beforehand. I used to think I did not get opportunities like other people did and that I was just unlucky, but looking back, this was not true. I have had opportunities - the problem was, I wasn't prepared to take them ahead of time.
Don't let people tell you that you are something or some way, put you in a box and tell you that is all you are and all you can ever be if that category is not who you want to be. Also don't do it to yourself. Don't think you have to stick to something because "that's just who you are and have always been" if it isn't taking you where you want to go. You can change the kind of person you are, you can change "you". You have more power than you think.
Be careful what you say, because once things are said, you can't take them back. I'm talking especially about getting into arguments with family and friends and saying angry, hurtful things in the heat of the moment that you really don't mean, and you come to regret it later because sometimes you can really hurt someone's feelings. There are quite a few things I've said and feelings I've hurt that I wish I could un-say and un-do.
For those of you who have pets - always remember to treasure your time with them. The time goes much, much too quickly.