My advice for the beginning MACHINIMATOR
Besides Oxhorn's guide, the best piece of advice I have for the beginning machinimator, whether it be WoW, Halo, TF2, or whatever you like, is the following....
DON'T START WITH YOUR DREAM PROJECT FIRST.
If you're never made anything before, you'll find that you'll keep going back and remaking scenes you've already done over and over as you learn more and more, wasting a whole lot of time on something you love. In the end, you will have seen messed with the same material for so long and so often, you'll be sick of it. Hell, you'll see it over and over enough times when your production is going right.
I'm speaking from experience here. When REKGAR & BUSBY was rounding third base and heading for home, I kept thinking I had tried too much, too fast. There were technical things that I wasn't happy with (compositing :( ) that could have been fixed if I had spent a bit more time practicing the techniques. But I had been working on it for so long, I got to the point where I just wanted it to be done before I filed it away with the hundreds of other personal projects that I've never finished. Fortunately for me, I produced something that people have liked despite its flaws and that has given me the confidence to move forward...after some more practice with the fundamentals, of course :)
So to summarize for the beginner...
I suggest working in small steps with quick little projects so you can learn the various individual aspects of machinima. Music videos, for example, are a good place to start, IMO. They help with learning to edit and familiarize yourself with the tools in your editing program ( this is ALWAYS a plus).
From there, write and shoot some short scenes to help more with the editing and working with dialogue and putting them all together. These short scenes also help you learn to tell a story on screen.
Get some practice before you dive head first into the machinima for the ages. I think you'll be happier in the long run.
I hope this helps...somebody.
^JR^