What can I do on my off days to improve faster?

It has been a while since I have done strength training but I recently started doing the recommended routine. My schedule looks like...

Sunday: Strength Training, HIIT sprints

Monday Rest

Tuesday: Strength training, HIIT sprints

Wednesday: Rest

Thursday: Rest

Friday: Strength training, HIIT sprints

Saturday: Rest

I was considering adding light cardio to my rest days but is there anything else I can do on the days I am not strength training to better my improvement?