Before doing Acamana one has to wash the hand and feet and then be seated in kukkutasana (a particular ascetic posture for religious practices) posture facing east or north. One should take a little water in the palm and chant acutAya namaH, anantAya namaH, etc., and sip the water (prAshanam). These are the important observances. After doing this thrice, one must wipe the mouth and wash the hand clean. These details can be read in Ahnika grantham-s.
There are many occasions during which one must do Acamana. This should be done as a component of any karma during the beginning, middle, and end. One has to do acamana before partaking food and after having food. After attending to a nature’s call (shanka nivrutti), one has to wash hands, feet and mouth immediately after and perform acamana. There are instances when acamana has to be done as a component of relevant karma-s as stated. It is been said, even while going to a temple one has to do acamana to ensure one’s purity. If possible one can observe them.