I like Dave Wekl's explanation of his technique here...
http://www.youtube.com/watch?v=KTOVLkp-nOI
As mentioned above concentrate on staying balanced, and slow things right down to a tempo where you can play evenly and as perfectly as possible (use a metrenome of course). This is the tempo that you should be practicing at for extended periods of time, like 20 - 30 mins a day of single stroke rolling if you can spare the time.
Then if you want to try playing faster, only do it for limited periods of time, because if you play consistently at tempo's that you are not comforatable with then you are only programming bad technique into your muscle memory. Also to increase your control, do rudiments with your feet, particularly paradiddles. I personally only practice for extended periods of time at very slow speeds, so I do 20 - 30 mins of single strokes a day at 40bpm in 16th's, though I do play to songs that have lots of fast double bass in them as well.
Seat position, throne height, the angle of your legs, spring tension and where your feet are on the pedal are big factors so play around with these until you find a good position. Personally, I like my spring tension to be loose, but still tight enough to pull the beater back, I like my lower legs to be angled forward slightly with the top of my legs parallel to the ground. I also sit on the edge of my seat as Dave weckl mentions, cause it make's me feel more balanced, and I have my feet about 2 -3 inches down the pedal so the beater comes back on it's own. This actually means that I sit quite far back from the kit, but I can still reach everything easily.
If you really want to sort your foot technique out, then I suggest Matt Ritter's 'Unburying the beater' DVD, it really sorted my feet out! I think Tim waterson (fastest feet title holder) has a DVD out too which should be very informative.
As for which technique to use, well I recommend heel up as I find it most comfortable, you'll find that at slower speeds you'll be using your whole leg, but as you get faster you'll start to use more ankle. If you can, try to practice this ankle motion at slower speeds because it will really help you get faster. For double strokes, try out heel toe as mentioned in the Derrick Pope video that antiunderscores posted, you might want to leave this out till your a bit more comfortable on the pedals though.
