MY VERY FIRST DAY OF HIGH SCHOOL:
Here are my resolutions:
Say hello anytime I see an acquaintance.
Because I was always smiling and greeting the people I knew, people automatically assumed I was friendly (though I am not naturally sociable). And high school kids want to be friends with sociable people.
Take the first step.
All the girls there already knew each other - they didn't need another friend. But I did, so I had to make the effort. I had to be the first one to invite somebody to go with me to a movie, or over to my house. Once I did, they started to respond in kind.
Make friends slowly.
I couldn't get discouraged when it took a while to make friends. Hey, I had already waited an entire year, what's a couple more months? Making new friends is hard.
Use classes to get to know people.
I met most of my first friends because I sat next to them in class. Class (before, after, or even during class-time!) is a great opportunity to strike up a conversation, ask for homework help, or even better, to extend help when needed.
Hide my fear.
I was terrified coming back to school sophomore year. But acting confident really helped. First of all, acting confident actually made me confident. And second, confidence implies a lack of concern for other people's opinion, which paradoxically, makes others value your opinion more. High school kids are odd in that way.
Above all, remember that it can and will get better. You may have to work a little to make your high school experience a great one, but it's absolutely worth it!