The stoners will always welcome you into their group, as long as you have money for drugs. You'll pay dearly in several different ways if that's the group you choose to associate with. I am not speaking from a textbook, either. I learned a lot about human nature in the drug culture that most poeple will never understand. Let's just leave it at that.
As far as social circles, the easiest way is to try to make friends with a single person in the group and then see if they invite you to stuff that the group is doing. You don't need to be cool with an entire group to become part of a group. This same way of targeting specific people you think you'll get along with and then getting to know them works in high school, college, and during your adult life.
If you want to throw a party, you need to go to a few of them first. You need to see what it takes to get the word out, get the booze (and since you're 16, I'm officially recommending that you do not involve alcohol), and CLEAN UP afterwards. If it's at your parents' house, assume something will be stolen if it's a large party. I do not recommend throwing parties, unless you're already friends with many, many people.
It's really, really tough to meet people at other schools without some kind of common interest. The easiest way to do this is to actually find a hobby or sport that engages people from different schools/areas so that you can actually meet these people in a reasonable setting.