No. One of the easiest words in the human vocabulary.
People told you 'no' when you were in trouble, when you couldn't have something, and when you were wrong. So you learned it and you say "no" a lot. We live in a world of no.
STOP SAYING NO.
When you say "no" you're missing out on a chance. What chance is that? Who knows. Maybe it was life changing but you'll never know because you decided that it wasn't for you. I get it, it's hard to step outside your comfort zone but you know... it might be worth it. Don't stall your life with "no."
I personally am the worst at saying "no" when it comes to relationships. I don't know why, I'm not shallow... I just hate opening up and making myself vulnerable because I've been hurt so many times before. I know what you're thinking, "it's just the beginning, you're young... you don't know what hurt is." But boy, do I. I've been hurt by the cute guy, the athletic guy, the frat star, the druggie, and the "nice" guy. Some of those were the same person, so don't think that I'm THAT popular with the guys... which I'm not, so that should be a reason to not be so darn picky.
You know that guy you wouldn't go see a movie with or that trip you canceled because no one would go with you? Yeah, forget about that... Text him, NOW, and tell him you want to take your raincheck on that movie. Go down to the river and read in the sun, enjoy a day to yourself. Say "yes" and wait for everything to fall in place.
Make this summer the summer for "yes". Take a spontaneous trip with your friends, go see a movie by yourself, date, and have fun. Just keep saying "yes." The world opens up when you do. Don't stay at home wishing your ex will text you, making plans, or watching tv. Get up and do something, no matter what it is.
Now, I'm not saying that you should say "yes" to everything. Like if someone offers you drugs... that's a good time to say "no," but I'm sure you already knew that. I'm asking you to say "yes" to the little things that could change your mood, life, and friendships. Just remember what John Lennon said, "Life is what happens while you are busy making other plans." So go out and just live your life.