How can I relax my body fully? I constantly feel tension in my legs or even face muscles. Do you have any advice on this?

For me yoga does wonders. A short breathing exercise then yoga. If you can meditate in between… even better.
Eat foods high in magnesium. That helps too.

I am the same way if I forget to practice intentional breathing exercises throughout the day. I suggest taking time to breathe separate from meditation so that when you sit down to meditate your body is ready to get relaxed. Intentional breathing throughout the day will also help with anxiety and helps relieve stress that is stuck inside our bodies.

Ok to start off relaxing your full body I would start with trying to relax my face. I encourage you to do face exercises. For example: open your mouth starting with a smiling motion working it open to a full yawn motion. I would do thy about five times. See how your face feels after you try that. Moving to your legs I would give them a full message/ rub down after you get out of a warm bath. You’re going to run them down with and oil that smells good. This will also help you relax other areas in your body. I believe. That’s my take on getting your whole body intensed.

There are many methods I’ve used to relax: progressive relaxation where you tense a muscle group and hold it for a short time, then let go and feel the relaxation; a trick to relax the jaw muscles is to keep your tongue touching the roof of your mouth; yoga, especially Yin yoga; a good work out followed by a nice bath; sitting in a hot tub or sauna followed by a cold plunge; guided meditations; I’m sure there're more.

If you are talking about tension during the whole day… my suggestion would be to practice some of the items above and get to know what relaxation feels like to you. The, when you find yourself tense while driving or at work, remember what your relaxation felt like in the tense area of your body.

A good method is to lay down and scan each body part and relax them, starting from your toes, moving up to your ankles, calves, knees and relaxing your body bit by bit. It takes practice, so don’t get discouraged! Another method is to lay down and tense every muscle in your body for 5-10 seconds and release them all at once into relaxation.