When entering the zendo bow lightly with your hands in gassho (palms together, fingers up), and step in with the left foot first. The path you take to your seat should be just a foot or so in front of the row of cushions. Any turn you make should be made squarely in the corners instead of in a sweeping radius. Your pace should be respectfully metered and deliberate but otherwise normal.
At the designated time, the han (a wooden plank drum) will be struck in a prescribed manner in three rounds as a call to formal meditation. Immediately afterwards, a bell is struck three times, signaling the beginning of zazen. By the time the han is on the second roll down, you should be seated and in correct posture. When the bell is struck for the third time, you should be completely "adjusted" so that you have no further need to move throughout the course of the meditation period.
When the time comes to leave, rise following along with the leader and turn in the direction of the altar, to face your seat. If you are using a cushion, fluff it back into shape and brush away any hair or dust. Bow to your bench or cushion, turn clockwise to face into the room, and bow to the sangha. Exiting the zendo is done in alternating sequence from front to back. Each person in sequence following the lead of the meditation leader.
Note: If you have any problems with the recommended Zendo Etiquette and sitting postures please adjust accordingly. What is important is that you are comfortable with your participation and meditative posture. Being Quiet and Mindful should be your foremost considerations.