That's it. Lexi absolutely nailed it right here.
There are many things you can do in order to keep a relationship, it takes effort, patience and dedication. But to find a relationship to begin with? Completely different story.
Relationships happen, it's not something you can engineer, it's not something you can control. They just happen. And this is not true JUST for love, but for all kinds of relationships as well: do you have any good friends? If so, an you tell us the strategy you adopted to make them become your friends? No you can't, that's the point I am trying to make. You meet people, you are natural around them, and eventually something that is impossible to explain with words happens, and then you are friends. Love is the same thing. If you approach a girl with a plan in your mind, if you do not what comes natural, but rather a series of actions you had schemed beforehand specifically in the hope of making her fall for you, you have already lost. It will never work, simply because there aren't two people in this world who are the same, so the actions you have schemed, specifically to attract the attention of girls, might be exactly what that particular girl hates.
You need to be natural. You need to be yourself and yes, I am aware that it sounds very stereotypical and cliché, but that's how it is. If a girl does not like your true self, then a relationship with her is impossible. Trying to pretend to be someone else won't work for two reasons: there is no guarantee the girl will like the person you are pretending to be either, and even if she does, the truth will emerge eventually.
Of course you might argue "I have been myself with lots of girls and non of them liked me" but well, I am afraid that is something that cannot be cured. I mean, if a girl just does not like you, there is nothing to be done about it. The whole "insistence will win her heart" thing shown in movies is not only unrealistic, it is actually a crime (called "stalking") in real life. So if you are turned down, just don't give up and move on. It might feel disheartening on the long run, but you need to keep at it: you WILL find the one right for you eventually.
Judging from your profile, you are 18. You are still so young. Not finding love is not a tragedy at that age, and finding it only for it to end after a while is not a tragedy either: you still have a long way to go, try and enjoy what you get, instead of struggling in vain to get what is out of your reach. Go out in the vast world without thinking about anything, just be yourself, and you WILL find someone eventually.