I'm not the best at advice, but I'll tell you everything that may help that I tell others and myself.
I know you already stated you do this, but remember to always be yourself . You want to be able to find someone who likes you for you, not some fake image you make yourself out to be. Many people change when they get into HS because they want guys to like them. That's never a good idea, as it can draw the wrong attention from what they actually want. This leads to bad/toxic relationships, and just isn't good in the long run.
Most high schools are big with a large amount of people, which means many guys. Don't feel discouraged if one out of the bunch doesn't like you or rejects you. As I said, there is plenty. The hardest part is just finding that special someone.
A good way to get to know different guys is by, like Preach said, joining clubs and camps. Of course only join them if they interest you. Another way is by seeing if your friends have any guy friends and getting to know them. Since you'd most likely have mutual friends, it's probably more comfortable than getting to know some random stranger. Or, if there is someone you don't know that intrigues you, find out if you have mutual friends and learn about him from them.
If you want to approach a guy, keep it casual. Start with small talk to figure out his personality. Keep trying and attempt making a friendship. Don't rush into it. In fact, don't rush into any relationships. Start slow. This way you learn more about the person and you can tell if this is someone you want in your life or not. You can also try finding their social media accounts as well, either to add them or stalk them {Not literally, haha. You get what I mean. I'm guilty of profile stalking. Whoops.}
I can't really say much for flirting, as I am the worst at that, but if you grow to like someone, maybe try dropping very small hints and see how they respond.
That's all I really have to say. Sorry that this was kind of all over the place. I wanted to include a bit of advice for everything. Good luck with it, and if you ever need any more advice, feel free to pm me if you wish!