Fitting in can be really hard in middle school. But it's important to keep in mind that it's not about being someone that someone else wants you to be. It's about finding people that like you for who you are. And honestly, that definitely is a lot harder than it sounds.
Start by having confidence. That's a lot harder than it sounds, too. But if you like yourself, other people will like you. What you're trying to do, is find other people who like you for who you are. Get involved. If all of your classmates are talking about a new TV show, or they've all just read a really great book, read it or watch it. Don't pretend to like it, if you really don't like it, but at least you'll have a way to enter the conversation.
I understand that fitting in can be incredibly difficult. I have definitely been there. If you feel like you're failing at it, day after day, just remember that every new day is a new opportunity to try and fit in. It's important to understand that you don't have to be mean, you don't have to be someone you're not; you just have to be yourself. And if you feel like one day you really failed at that, just try again the next day, and you'll fit it before you know it.