Question
Rules for chanting Oṃ namo bhagavate Vāsudevāya
Answer
Who can chanta the mantra
Any Sincere Vaishnava can chant it regardless of caste creed or sex
The mantra Om Namo Bhagwate Vasudevaya is very first verse of Shrimad Bhagwatam, Shrimad Bhagwatam is a smriti, so there are no restrictions on who is eligible to recite.
The mantra is open to all, and anyone who is sincere Vaishanva can recite(do japa) it.
Or can any one chant this anywhere at anytime (while travelling, eating , Slipping , resting on bed) as we can do namasmaran.
The basic rules of japa must be followed, Vaishnava means one who has tan(body),mana(mind), atman(soul) everything dedicated or surrendered to Shriman Narayana.
A Vaishnava must maintain sattva, it can be maintained by sattvik food and everyday life discipline is must.
Everyday life discipline includes a specific place to chant(clean, neither too hot nor too cold, noise free zone) must be chosen, an asana of choice mostly kusha asana.
Bodily discipline basic sanitation, regular bathing, and achmana, celibacy, and following Dharma as in Dharma Shastras.
Time discipline Since I don't follow it I cannot comment on it, but one thing for sure sandhya kala and bramha muhurata are best timings
For travelling only bodily discipline is enough(while travelling even Dwijas are exempted from doing Sandhyavandanam).
Resting on bed : no, sleeping no, eating: yes(if you follow food discipline and eat prasadam, then food is ambrosia)
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