I had a lot of issues fitting in for a good part of my life. Luckily, over time after consistently working on myself, I've figured it out. You are definitely making a good step by discussing this here.

The thing I've noticed is trusting yourself in social situations. Trust that you have worth and that you don't need to change yourself to fit in. Know that you are special for being you. Accept that you have flaws, but so does everyone else. Don't over exert yourself with your shortcomings in mind and don't hold another individuals flaws against them. Don't change who you are for someone else. Be real, have fun, be supportive; things that friends do.

I hope this helps.