How can I work on my neutral game?

[Gaona]

I've been playing Mario for a long time now, and I must admit I've been playing like a noob. I'm going to study more Mario guides, even the basics. But are there any tips on how to work better on neutral? I find myself most of the time going in with Nair and Dair, which is by now a bad habit. I also don't use much of Up air because I don't know when to use it. Any tips at all are appreciated.