I cant really give much advice on this, but I can tell you my story and how I managed to get more into a popular social circle.
Pretty much, you have to find a CORE group of best friends, and stick with them the entire time. This is exactly what I had my freshman and sophmore year in highschool, a core group of about 5 guys that I always hung out with, and from there me and another group member would kinda expand the circle by getting chicks from either our school or another school to chill with us (me and him had the best game.)
We then started to chill with another core group of best friends, except they were girls (and they were a year younger than us : /. But hey, its a start). So then, it pretty much came down to every weekend my core group of best friends and the core group of girls would hang out together, thus forming a larger "social circle".
At the beginning of junior year, things started to improve even more. I had been friends with a pretty popular kid on my football team, and as the year went on, we went from friends, to really good friends, to GREAT friends. I think one of the main things that played a major role in strengthening our friendship was the fact that we both smoke weed. It would start out like every few weeks we would txt each other to chill, and I would bring not all, but a few of my core group friends (the ones that blazed) to go smoke with this kid.
Eventually, it got to the point where every weekend we would be chilling out at least once to smoke weed, and eventually I (since I was closest to him of my friends) would get invited to the popular parties of the school that this kid went to. From there, I would invite him to some of our parties, which where a ton of fun. Then from there, he would start bringing some more of his popular friends to come chill with us.
And eventually, it all comes down to now. Now my friends and I can easily get into the popular parties (as opposed to freshman and sophmore year wen we couldnt), and, we're not hanging out with those girls who are a year younger than us. Now we're hanging out with chicks our age, and some of them are pretty fvcking hot!
My point is, it's all about progression and moving up the social ladder. Getting into social circles is a very slow process, and it all starts by one person (like me) branching off to become friends with someone more popular, and then strengthening that friendship until you and your own friends are "in" the social circle.