Alright, here we go
Most metal drumming is rather simple with the hands, and down under is where it gets more difficult - but I'm sure you've observed that already. So there are 4 major techniques on the pedal:
1 - Heel down - I'm sure you're already familiar with this one already lol. Anyway, heel-down has negatives (not loud enough, and fast-tiring) and posetives (composed, more intricate and controlbale.)
2 - Heel-up - This is the one most metal drummers use. It's a very good technique to use for constant double bass strokes. It is also reasonable loud, and feels much better. Speed-wise, I think this and heel-down are on par with each other, ultimately - ultimately both muscles groups end up twitching spuratically. Think about this and try to figure out what I'm talking about, because by the time you get really fast, you're not coordinating the strokes one-by-one anymore - you just put pressure (body weight) on the ankle and you basically twitch. Anyways, heel-up is much easier to maintain, but it's hard at first. Heel-down will feel easier because you're used to it, but once you get that twitching things going you'll see the difference - it's almost in exhaustible. The bad thing is that it's pretty hard to get the gastroc muscles (muscles group used in heel-up) on the two legs to coordinate alternating stroke in twitching fashion that I explained, but you'll get it eventually.
3 - Swivel - This is basically heel up, but it's a very clever trick to allow you to keep track of what your feet are doing - because a lot of the time you'll notice your feet are going out of synch with each other - this method fixes that. So basically you're doing alternating strokes with the two feet, but this is how it goes:
L (swivel to left) R (swivel to left) L (swivel to right) R (swivel to right) etc etc
4 - Heel-toe - I absolutely love this method!!!1111111 You do a stroke with your heel, and come up for the double with the toe. There's two ways to do it:
1. Start heel-up (heel stroke first), end heel-up (toe stroke first.)
2. Start heel-down (toes stroke first), end heel down (heel stroke second.)
I use the first as I find it much more convenient to me as I'm normally in the heel-up position. But you can make up your own mind.
Anyways, by the time you get good with this technique, your feet will be doing a rocking fashion movement.
Now here's the best advice you'll get from me today:
Combine all 4 techniques in your playing:
-Heel-down for intricate strokes, or really short-lasting but quick strokes.
-Heel-down for endurance at high speeds.
-Heel-toe is so versatile, you can do anything with it!
-Swivel is less needed than the rest, but it's not bad to use once in a while.
Hope that helped, and if you got any questions, please ask - I tend to not make sense!
uke: 
