Don't do "cardio" on your off days if by cardio you mean running on a treadmill or hitting the stair master.
Does you gym have a prowler? If so, that pushing/pulling/dragging the prowler is great for an off day.
Also, hitting the weights but at a much lighter poundage is great for an off day. For example, if you normally bench 200 for 3 sets of 5, then hitting 150 for a bunch of sets of 3 is a great way to reduce residual soreness and get your body amped for the following day's workout.
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