You could go by feel. If you are feeling run down, then just do a normal workout and enjoy the extra day of rest afterward. But if you are feeling extra good, than throw in some extra volume since you have the extra day to recover.
James 1:16-17 ESV
Do not be deceived, my beloved brothers. Every good gift and every perfect gift is from above, coming down from the Father of lights
With God's help...Mens sana in corpore sano