This small work by Srimadacharya gives the procedure to be followed on Krishna jayanti((Krishnashtami) ,the rituals to be followed that day  starting from taking bath repeating the mantra given here and  the method of 'puja' to be done and other details such as 'tarpana' . Following these instructions with fasting on that day is a must for all Vaishnavas.

'KrishnAya VAsudEvAya dEvAya paramAtmane

Pranatah klesha nashAya GovindAya namO nama:h'