DO EAT ENOUGH.
DON'T RESTRICT OR OVEREAT.
I find that I am more hungry on rest days. Your body is quite literally repairing itself, this is the point of rest days. This takes energy, aka calories. So don't restrict yourself of calories because you're not actively burning calories by working out. Your body deserves the fuel; It requires it. In the same breath, make sure your food choices are high quality. Help your body help you.
DO LIGHT ACTIVITY.
DON'T BE SEDENTARY.
Light activity is always a good idea. Nothing too strenuous, but staying active will promote recovery, especially with sore muscles. Whenever my lower body muscles feel tight from a workout, going for a slow, short jog always makes them feel so much better. It sounds weird, I know, but the strides really help stretch my legs out, not to mention movement and blood flow help flush out some of those inflammatory chemicals that are contributing to soreness. WALKING IS SO POWERFUL. Just keep moving. Don't use rest day as an excuse to be a couch potato.
DON'T FEEL GUILTY FOR RESTING.
Your mind and your body deserve to rest. You're going all day everyday. Exercise is a stress on the body. Lifting weights is placing stress on your body. Life is both physically and mentally taxing. Stress has many not-so-great physiological effects on the body. Stress is already so hard to avoid, so help yourself by taking out the guilt of taking a rest day. Get all the benefits a rest day by fully embracing it and enjoying it.
DO MOBILITY AND STRETCHING.
DON'T DO INTENSE EXERCISES.
Sometimes keeping up with the routine of gym time daily is really important. Instead of breaking the routine, use that gym time to help promote recovery and work on bettering yourself and your physical capabilities with low-intensity movements like mobility work and stretching. Do not do intense cardio, HIIT, or resistance training.
DO STICK TO YOUR DAILY ROUTINE.
DON'T TAKE THE DAY OFF OF ALL HEALTHY HABITS.
Repeat after me: rest day is not an excuse to be lazy and eat garbage. Still move. Eat well. Hydrate. All of these healthy habit still matter, and frankly, this is the difference between living the lifestyle and it being "just a chore". Resting is just as important as training days; You need to have a good relationship with both. There is a lot of value in the doing this daily to maintain the routine.