Come out with a flirty vibe right away
Never try to sneak in under the radar. I don't know where guys got this fantasy from but i think it was created out of a need to stay safe while also meeting girls. there is no summer camp romance that turns into a lifelong romance...the guys at summer camp who made out with a bunch of girls (i'm hoping that's all that happened...i stopped going when i was 12) were pretty much the charismatic jerks but they certainly weren't the guys who played it safe and acted like pals then wanted to shift into dating.
Ignore the signposts your mind gives you
When you like a girl you're always looking for a sign she likes you back and that you should make a move. While this is fun to think about it's not always practical to real life and thus the scenario "oh...I thought we were just hanging out as friends..." Here's what you can trust--body language and does she flirt back at you. Also, while you're trying to figure out the signs of how you should get to know here another guy is taking the direct approach. Now, a lot of times the direct approach doesn't lead to a romance, but you can lose out simply because you didn't move on it. Find a quick way to be cute about it...if cute about it you must be but don't listen to some weird sign you think she gave you that she liked you because it doesn't mean anything. Her telling you that her boyfriend broke up with her is not a sign that she wants you to save her, sorry.
Be in Demand
Girls tend to be very concerned about the group think. You never want to appear like girls don't really get you or get into you. Sometimes this approach will work but often even lying about all the girls you get for some reason boosts interest in you. basically, anything you wouldn't want to hear from a girl she for some reason wants to hear from you in this regard. don't hide the fact that other girls find you attractive and she'll want to be a part of that club but at the same time don't seem like a player.
This is a damned effective but cheap tactic that can be used to sort of see where she's at with you. if you call her bro and she doesn't even flinch somewhat safe to say she's not into you but she could also just not mind being called a bro because she has a masculine streak. yet if you call a girl that likes you even a little bit a bro it's pretty damn insulting and either she'll call you gal or just get bothered by it which is a clear sign that she does not like getting friendzoned in this fashion. You also can do this more subtly by just not paying that much attention to her and having a fun, non interested vibe. this may seem to contradict coming out flirty but the ways don't have to be used all at once. they're alternate approaches to not being friendzoned. you can be direct or indirect about it and i would say overall being direct is faster and more ineffective and being indirect can potentially waste time but also is a lot more alluring then just being blunt about everything.