You have to be a decent mate to them first. Don't go out 'on the pull'. Instead, just get to know them in the context of wherever you meet - study, sport, music etc. If they think you have an ulterior motive then they'll back right off and you'll be back to square one.
Be patient. Some blokes go out with loads of girls from an early age and never find 'the one', and others maybe don't date until they're older than you, but end up with their perfect partner straightaway.