1. Never betray your integrity for any reason
2. Always maintain your self-respect, even if it means walking away from something or someone you think you want REALLY bad at that moment, later you will thank you.
3. Don't rush relationships to an end. Focus on spending time with people, having fun and connecting. If something comes from it, awesome, if not walk away and don't look back. If a woman doesn't want you (not just eh you're here, but if she doesn't crave for you), no matter how perfect she is in every other aspect, it's a dealbreaker.
4. At this age, securing financial stability and finding your place in the world should be your top priority. Let nothing distract you from this.
5. Don't shack up with a woman. This is enmeshing your life with someone else's and will make it much harder for you if the relationship ends or your life situation changes too much (likely to happen at this stage of your life). Also being around someone 24/7 without a lifelong commitment is a recipe for wasted years and heartbreak.
6. SAVE SAVE SAVE. Don't waste your money going out all the time, don't waste your money buying unnecessary gadgets and shit you'll still be paying for when you've grown tired of it. Get your money right before you even think about luxuries.
7. Reputation is important. Deal with people kindly, justly and with integrity and build a network of people you can call on (and who can call on you). Keep a small circle of vetted and trusted people close to you.
8. Don't dream, don't talk about what you're going to do when X. If you have a goal or an interest you'd like to pursue get to it quickly.
9. Always use protection. A few minutes of pleasure can give you a lifetime of responsibility and change the course of your life. That girl you're so in love with looks a lot different as a nagging baby's mother with her hand out 5, 10, 15 years down the road.