The key is to find where to lay your palm to get the best sound between muted and open strings. What I mean by that is if your palm is too close to the bridge, you'll get too much of an open string sound. The string will ring too much. On the other hand, if your hand is too far toward the neck, you'll kill the sound and you'll end up sounding more like a raking then an actual palm muting.
This will vary from guitar to guitar but hold a E5 and find the best spot by moving your hand from the neck to the bridge. At some point it will sound good to your ear.
Then there's the pressure applied. The more pressure from your muting hand, the less ring you'll. Sometimes adding more pressure will make for a more aggressive sound since you'll kill any reverb/ringing.
As for the actual movement, it's all in the wrist. You have to be careful and learn just how high you can move your hand before you loose the palm muting. I see the side of my hand touching the guitar (the part that does the actual palm muting) has being a pivot. The corner side (palm's up) where my hand meets my wrist should always be in contact when palm muting and my hand should rotate from there. Kinda hard to explain but hopefully that makes sense.
I also pick at an angle. Some people see this as bad form and tell you to play as perpendicular as possible.... I never agreed. I like picking at an angle because it adds an extra crunch in my sound. Since my pick is sliding a bit it adds some color.
In the beginning I said that you it's same approach if you are trying to mute 1-2 or 3 strings. By that I mean that if you use the same approach, when you are playing only one string, all the others will be muted thus limiting unwanted noise.
So hand placement, pressure, pivot and pick angle are for me the 4 ingredients to my palm muting.
I hope this helps you out