Answer:
You can try to get closer to them but if you all ready tried that and it didn't work, I'd say give up.
Step-by-step explanation:
Also don't rush things,
If they are your friend already and have been for a while, it can get awkward if you just out of no where try to date them.
You can give them hints, based of the person you might want to be subtle hints or very clear hints.
Also if they reject you, don't get mad at them, they have there reasons, and might even beat themself up for not liking you.