Popularity questions ..?

okay, so i'm about to go into highschool. i've got some sort of social phobia where when i'm with my friends i'm totally social and funny and everything, but when i'm with someone i don't know very well, i tend to feel insecure and shy. i'm really not popular, i have sort of a medeocre reputation in school, i've got about 6 close friends and i hangout with about 4 of them during recesses etc. then, theres a big popular group where about 50% of the kids in my grade level are. i know i'm pretty cause i've been told so many times. two years ago i went to a different school for grade 7, now i'm back at my old school in grade 8 so people have filled the gap where i use to be. i tried hanging out with the crowd, but i was too insecure and shy'd away. i need tips on being more sociable near people i dont know. any tips?