Very simple technique, used in conjunction with many practices. This is the Raja Yoga version….
(I am not covering the more advanced technique here – I don’t practice it…so…)
While sitting in any comfortable meditation pose, turn the tongue back (fold it upwards and backwards) so that the under surface of the tongue touches the back portion of the soft palate on the roof of the mouth. Let it rest there, relaxing the jaws, lips, and keeping the teeth a little apart…..That’s it, for now. You may read all sorts of things about getting it back into the nasal cavity etc…but not for now. It is sufficient just resting as described above. Do not strain.
If you feel discomfort, release it. Take some time to build up to being able to hold it for longer periods.
Khechari Mudra is usually practised with Ujjayi Pranayama……Khechari Mudra accentuates the pressure Ujjayi exerts on the carotid sinuses which regulate blood pressure.
Do not practice if you have tongue or mouth ulcers, or if it causes a bitter taste to be secreted.