First of all smile a lot and have more confidence in yourself. That way, you will look friendly, open, and approachable. People are usually drawn to those kinds, so try to present yourself as one.
Second thing is to be nice to others. This doesn't mean sucking up to them and giving everyone compliments. It means that you are fair to others and you won't judge them harshly. It also means that you are considerate and sympathetic to other people's feelings even if you don't want to be. This shows that you are not only nice, but also mature and understanding.
Third of all, don't be afraid to express yourself. Don't just go with the flow about what other people want out of you. You need to share your voice as well. So don't be scared to let people see who you are and what your opinions are. People will appreciate you for your thoughts. Those who don't aren't worth being your friends.
I hope this helps. Good luck!
