Don't get too close to other anchored boats. The wind can change and in a matter of minutes you can have fouled and tangled anchor lines, and hulls and dinghies banging against each other. I'll never forget the commotion caused one night off the Bitter End in the BVI when a late-arriving boat anchored too close to another. The shifting wind at 0300 caused them to tangle with one another and soon there were two angry and burly boaters on deck, sans clothing, but armed with spotlights, shouting and cursing while blinding each other with the lights. Speaking of spotlights, if you need to use one, make sure you don't inadvertently blind your neighbor.
Sound carries exceptionally well over water and many boaters retire early for an early departure.
Respect their right to sleep in peace. Also, remember that any comment you make may be heard. If you are using your dinghy at night to go to shore or visit others in the anchorage, do so using oars and not your outboard. Some boaters are friendly and like to socialize, while others are reflective and just want to be left alone. If you are rowing around the anchorage and see people on deck, you should be friendly but not intrusive unless, of course, encouraged.