I have to write this quickly because I must go to class.
This is a question I think everyone wants to know. But Zazen is Zazen. Every time you sit. That is a gate. a...something or other. It's like fist that's clenched and through Zazen that clenching relaxes or opens. Every time you sit is new Zazen. New.
As Heart Sutra says:
This gone is Dogen's Zen. Is our Zen. Anyway, gone is gone. Nothing to say. Sit. Let the the thoughts come and go, and sit. Just sit. And...sit.
This is just my limited experience with Zazen. I am not a great Zazen guy. But every time I sit, that is a gate (as in door, not "Gate" as in gone).
Anyway,that's it. Just that.
Sit in Zazen posture. Notice things. Be egotistical if you want, be an ass; however, Zazen will "always" be right there. And we can't ignore the fact that Zazen is not like that.
Anyway (again), Dogen gave some great tips. Like sit in lotus, and study the self, and so on. Gautama Buddha gave some great tips (Heart Sutra). A lot of people gave some great tips.
I hope you continue to sit Zazen and have fun or whatever it is that you do. I know I will, or hopefully it will be that way.
Anyway (third time if your counting), have to go to class.