Three things have helped me recently to gain a lot more speed (although I’m not that quick, just don’t mince along making lots of mistakes like I did).
I’m assuming you’re talking about going downhill here as well.
Since I started riding my hardtail more I’ve become a lot quicker and make far fewer mistakes and it’s helped me learn what works for me (along with a few tips from Brian Lopes’s book).
I now have a mantra in my head before big descents:
Relax, look as far ahead as possible, aim to achieve perfect balance on the bike.
The biggest thing that helped me was to look far ahead so I’m always planning for what comes next. The better balance has come from riding a hardtail more and just practice. It’s great being perfectly balanced on the bike and knowing where to put your weight during cornering etc. This is the most fun part for me especially if you get the bike drifting.
I think like with any ‘sport’ it’s good to have a simple mantra to say to yourself at the start. Like I used to be really bad at football but got better when I said to myself ‘don’t give the ball away, easy passes’.
Get the basics right and the rest will follow, hopefully. That’s what I think anyway. And have fun.