Here is an old writeup with respect to Gurmat Ishnaan:
1) We should get up at amritvela. (Around 2am).
2) We should try to clean our stomach (through excretion) before doing ishnaan.
3) We should brush our teeth (or use daatun).
4) Tie our keski to our waist, wrap Siri Sahib (kirpaan) around keski and also keep your kanga there. Open our kesh.
5) Use full cold water (no hot water at all) and wash your hair and face. In Canada, water is ice-cold in summer and winter. The feeling after taking shower in cold water is amazing. Consciousness reaches it's maximum. Abhyaas goes automatically.
6) After washing your hair, soak out water and comb your hair and beard. Wash your kanga and place in in your jooRa (hair knot). Tie your keski ( a new one, a fresh one) on your head.
7) Wash your Siri Sahib and Gaatra or use your second set of washed gaatra and Siri Sahib and tie it around your head.
8) Now do ishnaan of your body, again with pure cold water. Such is the affect of cold water (ice cold water) that automatically swaas swaas simran abhyaas starts in full force. The feeling after ishnaan with cold water is undescribible (beyond description).
9) Keep separate towels for your body and hair. Use your body wala towel and dry your body.
10) Remove your kachherra and ensure that the right leg is removed first. Keep the wet kachhera in your left leg for now.
11) Take your new (fresh) kachhera (must be white kachherra, long till knees) and place your right foot or leg in the new kachherra. Now remove your left leg from the wet kachherra and wear your left leg in the new kachherra.
12) All the time while we do ishnaan we must do either Siri Jap jee Sahib or Vaheguru Gurmantra or Mool Mantra or any other Baani e.g. Siri Basant kee Vaar. Otherwise Guru Sahib does not accept ishnaan dee sewa.
Note: As per the aforementioned, head should be washed first but subsequent to writing the above post many years ago, senior Gursikhs from India clarified that it is okay to wash your body first.
Bhul chukk dee maafi.
Daas,
Kulbir Singh