Prasadam Etiquette:
Wash hands and mouth before and after taking prasadam. In the Western countries it may be difficult to wash our feet. But when in India, it is recommended that you wash both your hands and your feet before and after taking prasada. Use the right hand for eating and drinking. Even if you are a lefty, try to use your right hand.
When a devotee distributes prasada, remnants of food offered to the Supreme Personality of Godhead, in order to maintain our spirit of devotional service we must accept this prasada as the Lord's grace received through the pure devotees. (NI Text 4, p 39)
Remember that Krsna prasadam is non-different from Krsna. Recite the 'sarira avidya-jal' prayer to remember that. Meditate on how Krsna tasted the offering and His mercy in providing prasadam to us.
Wash hands after drinking water.This is done because when your hold your cup while drinking, your hands actually become contaminated. Any items that need to be sucked while eating should be gracefully removed with the hand when done and should not be spit out in the plate.
After one takes prasadam the area where the plate was kept must be cleared of any grains that may have fallen while eating. One should not step over the area where prasadam was taken, because it is considered contaminated.