Friendzone exists for guys in the 'maybe' category, they know the guy likes them and it's a safe fall back when everything else fails while it boosts their confidence/ego withevery subtle hint the guy drops.
If the guy goes all out and stops being subtle but things arent bad enough yet, or if she really isn't interested in anything more than someone to boost their ego, listen to guy problems or do things for them, she always has the "you're perfect but I don't want to ruin our friendship" (this excuse will be forgotten instantly if things change in the power if balance)
Ways to change the power of balance include:
Physical appearance, guys that go from the geeky pimply nerd to the gym stud all of the sudden find the friendzone disappearing now she can see your personality
Money, goes without saying that even women who aren't gold diggers still will make excuses to themselves why you're datable now, as opposed to broke you who she wouldn't date. The idea is to work hard and save your money, don't overspend, women instinctively are attracted to men who can provide, it's true in all of nature's animals. (Don't overspend or shower with gifts for no reason or you'll end up getting a gold digger who doesn't respect you and will move on when something better comes along)
Confidence, women are attracted to guys more about perception than looks (to an extent), where guys are more about physical attraction, women are more about perception, hers. Women like a guy who flirts confidently in a joking manner then plays it cool, backs off and makes her unsure if you were serious or just messing, the idea is to plant the seed and walk away, it will die quick if you're just standing on it, menand especially women are less attracted to what they know they can get.
Easiest way to see if she's at all interested, and keeping you around as maybe a backup instead of just her brother type friend is to be nice, but not too nice, never be short or upset when she tells you things even if they upset you, then when the times right subtly flirt with one of her friends, not to obvious because women notice everything, even all the subtle hints she pretended not to notice you dropping on her, use one of those same subtle flirting on her friend and see how/if she reacts.
Tells you bad things about her friend out of nowhere or stops hanging out with her and you at the same time, your foots in the door.
Doesn't seem to notice, care, move on. if it really bothers you take solice knowing ust wait 10yrs for a few bad relationships, kids and pounds later when they come around wondering why they couldn't meet a nice guy like you...
Sorry... Way too long but I typed too long to just delete it... Potato.