I'm learning tremolo picking and until now I've been resting my palm just above E string and anchoring with my pinky. I noticed that when picking 2 strings at the same time I also mute the first of the two (which is not good). So I read that I should not be anchoring and right hand should float and not touch guitar at all! But it seems impossible to pick that way. What is the correct right hand placement when doing tremolo picking?
There is no single correct way to do tremolo-picking. If you analyze how the greats do it you'll realize that everybody has their own technique. I'd suggest to watch videos of relevant players, and analyze their picking hand technique.
From my personal experience as a teacher I know that lifting your palm but anchoring with one or two fingers (around where the volume knob usually is) works well for many guitarists. I personally anchor my right-hand pinky and ring finger under the volume know while my palm doesn't touch the guitar.
Many guitarists, including myself, anchor a pinky onto the pick guard in order to retain accuracy when tremolo picking.
Some of the top guitarists, however (I'm including Malmsteen, Vai and others) don't anchor at all, they hold their hand clear of the guitar and use both forearm and wrist, which allows them much faster pick speeds than an anchored hand.
What works for me is to lightly keep my palm (the bit for palm-muting) just behind the bridge, and anchor the forearm to the guitar. That way, there's a whole hand movement available, which is a little stymied when the pinkie is resting on the guitar. Also, it's easier to move to other strings. Anchoring around a knob means too much stretching if one needs to play lower strings. Works well for the top two, though.
Whenever learning a new technique it's best to start with slow and deliberate practice keeping a relaxed hand movement. Shake your hand out sideways and with a flapping motion before you start, and at regular intervals to keep from tensing up. It will feel really strange at first, but after a while you'll get the hang of it and it will actually improve all of your other playing techniques. It helps to watch videos of mandolin players who also use lots of tremolo and fast picking technique.
I went through the same thing too when I hit a dead end as a "locked wrist-anchored palm" player. Gradually I was able to develop a floating right hand technique. I still palm mute when I need to, but I can also tremolo-both single and double strings, arpeggio, play intervallically, finger style, slap, etc. which require lots of right hand freedom. Just be patient with yourself and you will eventually get it! Best wishes...
whether or not you should anchor depends on the speed you're aiming for and your musical goals really. for anyone who plans on being a master shredder on the electric will need to be as efficient as possible and as clean as possible. so optimally the only thing touching the guitar near the bridge is your wrist. hears why:
Max Speed. anchoring your pinky or any other finger to the body or bridge will place a severe restriction on your max speed, which will then be overcome by switching to a position without the anchored finger. a good example of this is john petrucci. he anchors for the slower parts and removes the anchor to pick fast. the problem here is this will force the brain to remember an entirely different set of muscle memory for different picking speeds, possibly a HUGE barrier for growth down the road. it also makes it near impossible to sync the tremolo picking technique with the left hand for solid alternate picking without adopting the non-anchored technique for slower speeds. so why not simply remove the anchor in the first place? there is a definite increase in picking consistency when you get used to playing without it as well as increased mobility (ex: string skipping, sweep tapping, anything with big right hand movements)
Muting. since you tagged "metal" i'm assuming you plan on using significant gain at some point. few things sound worse than accidentally hitting an open string in this situation, and this happens live more than it does in practice and more than we admit. to prevent this use the fat of your right hand (preferably the palm but thumb works too) to mute the strings below the one you are playing on. if you know how to palm mute its the same thing, just avoid muting the string you're playing on. this technique can than be used in conjunction with most others to give much cleaner performances.
ideally your form for tremolo picking should be the same as your normal picking technique just faster. many of the best guitarist in the world(i.e marco sfogli, paul wardingham, rick graham etc.) have proven its more than just possible, its accurate and efficient.