play I Am The Black Wizards over and over
I think you were joking, but that's actually a good song to get your picking used to...at least the Nightside Eclipse version and not the live version because the live version is quite fast.
OK, ENOUGH OF ALL THE BULLSHIT, RIGHT? CHECK IT OUT...
I pride myself on my rhythm abilities, so I paid extra special attention every time I practiced for the past few years...it may not work for you, but it worked for me...and there are few songs that I have trouble playing rhythmically as far as fast alternate picking goes. I just learned Do Not Speak by Anaal Nathrakh and it's much easier than you think. I'll just tell you MY personal method, and you can take it or leave it because everyone here is correct...just choose what you like. Here we go:
WARM UP FOR NO LESS THAN 30 MINUTES!!!!! Did you catch that? Let me repeat it again: WARM UP FOR NO LESS THAN 30 MINUTES!!!! I'm not talking doing fucking jumping jacks, either. Stretch for a couple of minutes and get loose. Then we have the Chromatic Scale...play it. A lot. All the way up the neck and down, ascending and descending, back and forth for about 15 minutes...DOWN PICKED AT AVERAGE SPEED. After those 15 minutes of comfortable picking are up, you should start to feel loose in both hands and knock all the dust off yer fingers by then. Repeat for the next 15 minutes the Chromatic Scale, only this time completely alternately picked AND CLEAN! If you fuck up once, JUST ONCE, go all the way back and start over again. I recommend watching tv or something while doing this because it's quite boring, but it fuckin' works, I promise. Again, ascending and descending, up and down the neck for the next 15 minutes playing the Chromatic Scale. It stretches your left and right hands, which is great.
Positioning...the fact is, you want to use as least amount of elbow as you can because in 20 years you won't be able to pick up a guitar if you play straight from the elbow. You should be completely relaxed in your playing, no matter what position, however. Karl Sanders plays with only his fingers, rarely even moving his wrist. Many jazz players play that way and for more legato stuff and needing a light touch sometimes, this is a good method. I personally plant my hand where it needs to be according to the song. If it needs strong palm muting, I'll slam it down there, but at the same time I'm completely loose and comfortable. You want to feel as if you could do it all day long with little effort. If you're feeling pain or out of breath, you're probably too tense. That said, you've still got to do what's comfortable for you...I'm just trying to give you an idea.
Ok, so we're warmed up now. The next thing I do is choose a song that's a good warm up thrash metal song from the 80's...those are usually quite simple rhythmically and very dynamic at the same time. They usually are basic power chords with lots of tremolo picking. For warming up rhythmically, I first play Damage, Inc. by Metallica, then Hangar 18 by Megadeth, and maybe a couple of songs from my old band with our demo in the background. Every person is different, but I don't feel completely loose until about 35-40 minutes into playing. I can rip right into it cold, but sometimes I'll skip a down or up pick by accident if I'm not ready. You gotta remember that this isn't Poison...it's extreme metal.
Solos are how you want. I prefer slow and melodic solos anyway, so I usually start out by playing Time and Mother by Pink Floyd...just the solo parts. Really easy stuff...then I move on when I feel a little more relaxed to the lead break in Opeth's "When"; I fucking love that solo. I suck at sweep picking, so I just alternate pick everything. After this, I'm good to go.
It's all up to you and what makes you comfortable. Pick and choose what works best for you...we're here only to give you ideas. Good luck and have fun!!!!