The keystrokes Alt+1, Alt+2, Alt+3 and Alt+4 are used to move notes into
different voices.  If there is a note in the voice you're  moving the note
into, the existing note will be overwritten so, be careful about using them.

When you tab along or use the arrow keys, the top note of each chord is
selected.

Another trick for selecting notes in chords is to use Alt+Control+1, +2, and
+3 to select the first, second and third notes in a chord.  Alt+Control+B
selects the bottom note regardless of the number of notes in the chord.

This can be useful if you want to strip all of the highest notes away.  Just
select a number of bars on the staff and then press Alt+Control+1.  You can
then cut the selected notes and if you want, paste them to another staff to
give you the top line.