Practice, Practice, Practice, Practice, Practice, Practice, Practice ... and um, hmm ... Practice! XD Seriously, it's the best way. Also, doing a lot of tutorials is great.
However, actually learn to take something from those tutorials and incorporate a technique into your own design. I've seen way too many copycats on deviantART who all apparently did the same tutorial and they did little [if anything] to further enhance their project.
I've actually just purschased
IconResource last night because I want to further my knowledge about icon creation.