If I think about it, I can look back on every relationship (even the insignificant ones) and identify some sort of lesson I learned. It could be something simple like, I don't really care for boys who cannot properly pronounce the word "library," or something colossally important like, if I think he's cheating, he probably is. Sometimes the lesson is just, hey I'm not hung up on the last guy before him as badly as I thought I was—he helped me move on.
The thing about these lessons, is that if we don't heed them, they'll keep presenting themselves to us. They want to be learned. However, as a relatively seasoned lesson-learner, there are two I think everyone needs to focus on mastering...
1. If you don't value yourself, no one else will. We all want Prince Charming sweep us off our feet, rush us to the altar and plant his charismatic, royal seed in our lonely, weepy womb. However, that does not mean we should compromise everything we think is important to cater to Princie's needs. We should not give up time with our friends or family to be at his beck and call. We should not allow his fickle feelings to dictate our self worth. We're supposed to be the princesses in this scenario—and if he isn't going to treat us as such, he isn't worth our time. Our value is immeasurable. We need to acknowledge this and treat ourselves with the respect we deserve.
2. Always trust your intuition. It is sooooo easy to silence that little voice in our heads that says, "I really don't like the fact that he's discombobulated and always late." Or, "he's great on paper, but I'm really not that attracted to him." We're so anxious to find Mr. Right that we choose to ignore the red flags in hopes that maybe all his other great attributes will turn them green or blue. But if we're honest with ourselves—really honest—we can usually save time and heartache by just admitting he's not the right fit. Your gut knows what's up. Listen to it.
And if you think there is a lesson to be learned from a past relationship, listen to that too. Or else history will surely repeat itself.