To be honest half the girls I've gone out with have asked me out, one of them, I asked on a date after waiting for 5 months to get the nerve to ask her. What I've found helps the MOST is CONVERSATION. ALWAYS engage in conversation, try to text her as much as possible. Be funny, sweet and nice, or I mean, be you. Most of these people, I talked to them consistently for at least a month and they started to have feelings.
Be there for them as well, I'm really good at telling if something is wrong with someone but if you're not, then just try to be there for her as much as possible, be open and understanding. Also, try to hang out with her in person AS MUCH AS POSSIBLE. Any open opportunity, take it. Going to a coffee shop, walking around town, I can't come up with a lot of examples but it's extremely important that you hang out with that person as much as possible in person. I've honestly found the MOST important thing in starting a relationship and maintaining one is time. Without spending time with a person, how is it even a relationship? In a relationship you eventually start to grow apart and distant without it. You start missing the other more and more and it affects your relationship, despite how many phone calls or texting you may do, not enough time can ruin a relationship. In making a relationship, I mean, how are you supposed to begin to know each other? Those quirks and little things that you don't notice when you're texting someone, which is also really important as with some people, those little things made me like them the most.
After a while, they'll start to have feelings for you as well, depending on what type of personality you have but if you're a generally sweet, caring and open person, you'll grow on them, but don't annoy them by your presence, if they don't want to talk, you'll notice and don't force it on them or be pushy and if they don't have feelings for you, it's not the end of the world, there's other fish in the sea and probably, even better methods, this is just what's worked for me the most in the past.