3) Take diaphragmatic breathes. Never from your chest.
4) Your breathing should be so slow that even you should not hear it’s sound
5) Another exercise I do is @WimHof_Iceman method.There is WimHof app and it’s a guided exercise
You can read about breathing in The Oxygen Advantage by Patrick McKeown. I have also ordered - The new science of a lost art by James Nestor.