Just do a lot of home recordings. Don't enter any contests until you get a bit of feedback or until you're solidly happy with what you're coming up with. As some song MUST've said at some point - please yourself. Then go and try to please the rest. And check around this site for leads on other tips, other people to ask.
Advice is easy to give.
Harder to take. It's easier to be a critic than to write a perfect song. If it makes you feel all warm and gurgly, it is Your perfection. Some people like the Spice Girls. Some HATE them.