While worshipping Lord Vishnu, first of all a devotee should worship the ‘Asan’ of the deity by chanting–
Om Vasudeva Asanay Namah.
He should then make salutations to Lord Vishnu by chanting the following mantras– Om Vasudevay Murtaye Namah,
Om Aim Om Namo Bhagavate Vasudevay Namah, Om Am Om Namo Bhagavate Sankarshanay Namah, Om Aim Om Namo Bhagavate Pradyumnay Namah, Om Ah Om Namo Bhagavate Aniruddhay Namah
Subsequently, a devotee should worship the various incarnations of Lord Vishnu, his weapons as well as his different mounts by incorporating the rituals of ‘Shodashopachar’ and by chanting the following mantras–
Om Narayanay Namah,
Om Tatsad Brahmane Namah, Om Hoom Vishnave Namah,
Om Hraum Namo Bhagavate Nrisinhay Namah,
Om Bhuh Om Namo Bhagavate Varahay Namah, etc.