Here is a Video for Janmashtami Puja Vidhi (Gokulashtami Vrata Procedure). In 2017, Sri Krishna Janmashtami date is August 14/15. Ashtami Rohini is celebrated on September 13.
In Udupi Sri Krishna Temple also, Sri Krishna Jayanti is scheduled for September 13.
Here is the detailed Sri Krishna Janmashtami puja procedure with mantras. This Krishnashtami pooja vidhi article also includes the list of items or material required for Sri Krishna Gokulashtami Pujan. There will be slight differences in steps involved in Janmashtami puja procedure from place to place (South India & North India), but the generalized puja vidhanam is given here.
Check this video for detailed Janmashtami Puja Procedure with Mantras and fully explained Puja steps..