A simple progressive relaxation technique is to lay down, breathe in and tense everything, breathe out - let go - say the word "relax". Keep practicing until you can exhale, "relax", and the body follows. Its a good way to begin to feel the difference between tension and relaxation.
Standing Alexander Technique - lift up from the middle of the head and down from your center. Breathe, body scan, sense any tension, exhale, "relax". Also good for spinal alignment.
Standing meditation - tree hugging - can help trust the body structure and alignment to hold you up rather than the muscles holding you up.
Tenkan, tenkan, tenkan - letting go of tension.
IMHO, the real internal secret to relaxation is to find out what internal mental belief or habit we use to create and maintain the body tension to begin with - challenge it - let it go.
Hope this helps in some small way.