Look at the beginning of the piece and determine what the tempo is for the composition. If it is a numerical value, input that number into your metronome. If it is a tempo indication such as Andante or Allegro, look up the corresponding numerical value for that tempo in a musical dictionary.
Start the metronome and get a good feeling for the tempo of each click.
Press down on a keyboard key for the full value of the beat. Remove pressure at the end of the beat. If there is more than one quarter note, accent each one in the same way.