How to get faster?

I'm still new to MTBing...but I need to knwo the best way to get faster.
Is it just a matter of muscle strength??

How can I train to be faster?

Thanks for any ideas.
Christine

Ok, I already mentioned the riding with people slightly faster than yourself.
It's not necessarily strength, it's the fitness to spin, knowing what gear to be in when and not being afraid to descend like a bat out of hell. :D

Oh, and ride lots. :)