I would let my 16 year old self know that....
1. In ten years you're going to be single and it's going to be OK. You are going to have to get used to incessant questions and statements like "Are you dating? Why aren't you married? I have this single friend, can I set you up? Boys should like you. I'd date you if I were single". Don't let it frustrate you. Take it as a compliment. Sure you'll be sans husband and children, but you'll have plenty of other accomplishments under your belt. It's hard in the LDS culture to know exactly where your place is or what to do when you start getting "older" and you're still single, but just enjoy this time. Work hard. Save money. Have adventures.
2. People are going to hurt you, and you'll probably hurt a few yourself. When it comes to the ones who hurt you, stop worrying. They more than likely aren't worth your time. But for every person that does hurt you, there will be plenty of good friends who enjoy your company and would never think to be mean. Apologize to those you've hurt.
3. We all have to put in our time and work a job or several that may not be our first pick. Deal with it.
4. Try new things. Move to a new city. Take chances. You'll never know unless you put yourself out there. You might just land a job at a great company.
5. Friends will come and go and that's life. You did nothing wrong. Life progresses and we move on. It is not a reflection of you or how they view you. But just so you know, at 26 you'll have some great people in your life.
6. Take time for yourself. Do things you enjoy. You will never have this much time for you ever. Figure out your priorities and use your time accordingly.
7. Some things don't go as planned and that's just the truth of it. Learn how to handle disappointment without it getting you down because there will be plenty of it.
8. Learn how to laugh at yourself. If you can learn to laugh at yourself you'll be able to let things go faster. You'll be happier.
9. It's OK to be vulnerable. Confide in people. Trust that they care enough about you. It's scary, but it's worth it. If you just open up you'll see how many people really care about you and would be more than happy to help you.
10. Be happy. There will be trials. There will be stress. But stay positive. Stay happy.