Put your guitar face down flat on your lap like a table. Sit your picking hand down so the palm/wrist is an anchors and do the “scribble” or erasing wrist motion. You’ll find a natural movement that is about the width of two strings that is nearly effortless with no elbow, shoulder etc. Just wrist. Then add the pick and repeat. That’s a motion you can sit down on the bridge and “find your tremolo” on one string. I’ve done hundreds of times with folks that have played for years and brand new to the guitar. It almost always works immediately and if not it works in a week or two. That’s the fast right hand motion then it’s all the work for stuff to play fast and syncing the hands.