If I could talk to the 14 year old I once was....
1. Exercise regularly and eat healthy, and start doing it RIGHT NOW.
2. I know you don't like French now, but when you're in your 20s, most jobs you want will need it, so put up with it, and keep on taking it.
3. Keep your faith alive. If you feel it start to slip, reach out for help to other Christians. Just keep reading, and keep thinking, and keep attending church for goodness sake. It'll save you a LOT of grief later if you make Jesus Christ your best friend now.
4. Don't let fear hold you back from doing what you need to do. Life is FULL of 'what-if's', and most of them NEVER happen. Do everything to can to live your life to the fullest, and I can promise you, your family and BEST friends will be there for you every step of the way.
5. This one is the MOST important. Respect yourself, and respect your future spouse, and above all, respect God. You may come to a point, in your late teens or early 20s, where you feel like doing what everyone else is doing. Instead, hold tight and say NO when you WANT to say no. Oh, and keep saying YES to God. He's going to get you through a couple of VERY rough years, if you let Him.
6. Keep in close touch with your friends. If you don't, you'll regret it. I know you're an introvert by nature, but make a point of calling everyone at least once every two weeks. You'll be grateful when you're a bit older.
7. Spend as MUCH time as you can with your grandparents, and tell them you love them. Don't let your schedule, your activities, or your 'life' get in the way -- I hate to say it, but they won't be around forever, and you need to say everything you want to, right now.
8. Have fun. Do a couple crazy things -- not dangerous, not stupid, just innocently crazy.
You'll look back, and be glad you took that trip/went on that retreat/tried that new thing.
9. Forgive.... and do your BEST to forget. If you can't forget then just move on, in love, with those who hurt you.
10. Save your first kiss and your first date for someone OTHER than the first three guys you seriously like, starting in highschool and going forward. In fact, don't bother dating anyone OR kissing anyone who doesn't love Christ. I know that sounds prejudiced now..... but when you're 25 and looking back, you'll thank me.