The first thing you need to do is to ask yourself if there is something you like about that person. Is it the way that person talks? Does that person have an enchanting smile? Does that person have a really cool dressing sense? Is that person really decent and polite? Is that person really good at heart? Try to figure out what it is that can make someone feel attracted to that person and then pay attention to that thing the next time you meet them.
Instead of ignoring that person just because you do not like them, start paying close attention to everything they say. Not listening to a word that comes out of their mouth would not do you any good and in fact keep you from developing an interest in that person. Listen when they talk and soon you will find yourself enjoying what they say.
If that person is mean to you, try to think of a justification for their actions. There must be a reason for them to make fun of you. If they were rude to you, try to convince yourself that you must have done something that provoked them.
When you lie down in bed at night to sleep, try to convince yourself that you like that person by saying it out loud. Even if you do not like that person, repeating that you like her may eventually lead you into believing that you actually do like them.
Force the image of that person into your mind while listening to slow, romantic music. Create a scenario in which that person does something really sweet for you, something that makes your heart beat faster.
While hanging out with friends, bring up that person and start talking about something that person did or said.
Stare at that person and notice their expression and the movement of their hands. Some people look really cute while they are concentrating hard on something. Others look cute when they are sad or under stress.