I don't exactly know how to describe it, but I've been having trouble with fast strumming for years, especially triplets. Specifically, the style used in punk rock (think The Offspring). Both fast palm muting chords, and quickly strumming them openly. When I palm mute, my pick gets tripped up, and when I strum, I tend to accidentally hit other strings. And generally, I have trouble just with speed. What's the best way to practice for speed, and can anyone tell me what I might be doing wrong otherwise?

Examples that I have trouble with:

Half Truism-The Offspring
Fade to Black (the little part in the second half that goes 9-777-555-4442)
Quote by Jackal58
I eat dead meat all the time. You don't have to chase it around your plate and it doesn't try to peck your eyes out.

It Happens.

My Gear:

-Custom Fender MIM Black Strat
-Mesa/Boogie Rect-O-Verb
-Schecter C-1 Hellraiser
PRACTICE PRACTICE PRACTICE, : ) look at it this way, start as slow as u can and gradually speed up to the right pace, rather easy when u think of it, the only downfall is the fact that it takes time, but if u practice right the only thing that will come from it is perfection, remember tho, when u trem pick DO NOT use your forearm use your wrist, tho im one to talk cuz i still use my arm, but i try and catch myself and practice it properly, hope that helps, as far as hitting other strings, find a way of muting the strings with your hand, or jus use your wrist (you have more control in a small area doing so) but its different strokes for different folks, so find a way thats most suitable for u and go with it, jus make sure ur in time and accurate : )
Just practice, eventually it'll just click and you'll be able to pull it off.
You must slow it down though...if you just try to keep up with the original tempo you'll only develop sloppy technique.

Oh...and they're not triplets...triplets are notes that are of equal length. You're talking about what people like to call galloping.
Things with strings:
Ibanez J.Custom, Prestiges, RG8, SR5 bass etc
LP's, Strat, Tele
ENGL Retro Tube 50
5150 III 50W
Orange Terror Bass

Start slow, make the most efficient movements possible and gradually build your speed.

NEVER sacrifice cleanliness for speed. If you're hitting open strings you need to dial in your picking accuracy. The more discipline you have to stick to doing it right, the quicker you will improve, of course with practice and lots of it.

Also, play relaxed. A lot of people seem to want to tense up to go fast but it doesn't help and it could lead to you hurting yourself. Relaxed, smooth motions are your friend!

Good luck dude!