I only started going really fast (relative to me) this season and I am about 3 seasons in.
BIG thing for me, as another poster said, was don't be lazy and bend your knees. If I really want to bomb I get real low. It's not for wind resistence or anything like that, but my knees can absorb anything that comes up.
The other one for me is the board. I went from an all moutain freestyle board to a Never Summer Raptor, which is a great charging board. I am way more stable at fast speeds on that.