Playing hard to get is a great way of flirting as long as you show the guy that he is getting somewhere. If you give nothing, he'll just run away and look somewhere else.
Use it as a way of teasing him and building the attraction between you and a man.
Let your resistances drop when you feel the moment is ripe. If you overdo it, you just keep him hanging on and both of you will get nowhere, so be sure that building attraction and playing is the centre of your flirting style.