I'm a beginner at piano. When practising is it best to learn how
to play each hand separately at first and then put them
together, or to practice the whole thing? Or does it not matter?
When you are first learning something, you need to be able to
concentrate on just that single thing. This isn't something that
is isolated to learning a piece of music. If you isolate just
the single hand, you'll be able to learn it faster, without the
distraction of the other hand. Once you can play each hand by
itself, start out at a slow tempo putting both hands together.
Improve your speed as you are able. If you are a complete
beginner, you should be focusing on playing only one handed
pieces until the note reading and playing ability is reasonable.
After that, it depends on the nature of the piece. For example,
a study which focuses on right hand dexterity and simple left
hand accompaniment could possibly be played all together right
at the start. A slow piece with a low degree of technical
difficulty but higher expressi