How do you switch strings on the up stroke of alternate picking? Like in the master of puppets riff the goes two notes on the E string then one on the A string. If I alternate pick it I have a hard time going from the E to A because of the upstroke
you should really just downpick the master of puppets riff.

Practice with a metronome. You have to be articulate and precise in your picking. Start slow and work your way up. Eventually it just comes naturally.

The solution to most of these questions is really just practice.
ayy lmao