As a general rule:
To finish this lesson, here is a left hand exercise which will help your fingers to stretch and also help them become more independent. Keep each finger down on the string until it is required to play a note on the next string up, e.g., when you play the A note at the first fret on the 3rd string, your second, third and fourth fingers should remain on the 4th string, only moving across to the 3rd string one at a time as they are required to play the notes at the second, third and fourth frets on that string.