Know what you want really (don't care too much about a particular thing. It gets into your head, so forget it for some time - a week or so about the complete topic. It actually helps, but is real hard, lol
) and be confident.
Be optimistic, and don't be desperate or frustrated.
Be (or believe you are) awesome, have a decent personality, and you will be fine.
Edit: Also culture/country is an important factor. You can figure out more than we can, to be frank.
Edit: How do you know girls don't like you? Get a friend who is a girl. It usually helps.