The question of how to relax your muscles cannot be answered by telling yourself to relax.
It doesn’t work like that.
Deep relaxation is something passive. And you can’t consciously do it because it is the unconscious part of yourself that is relaxing.
It has to happen by itself.
The indirect, yet most effective way for how to relax your muscles is to consciously feel the tension that is already there without trying to change it.
If you hold that awareness of tension for long enough, it eventually dissipates by itself.
But you have to resist the urge to “do” something to “help” it.
All you can do is hold your awareness of the tension.
Now, if you must send any command, try this one:
My Wing Chun teacher in Hong Kong, Sigung Chu Shong Tin, didn’t speak English. But one night as he was guiding one of his students to relax their shoulder and the student couldn’t seem to do it, Sigung lightly tapped the student’s shoulder and said:
My fellow students and I loved hearing him speak English! And we found his choice of words quite curious.
It became clear to us that when someone tells you to “relax” it has the opposite effect. And it’s the same when you try to tell yourself.
You need time and space to be still.
That is, time and space to consciously hold your awareness of tension.
For this to happen, it’s important to consciously set up the parameters or conditions to allow the unconscious to let go.
Personally, apart from my Wing Chun training, I have found the most effective conditions to allow my muscles to relax in this fashion is via lying meditation.
More than likely, this means focusing on particular areas of your body one at a time, either in sequence or as they come to your attention. This is opposed to trying to relax everything straight away.
Again, most importantly, you need to give your body time and space to be still and just breathe.