Thought I'd start a thread so people can offer some good tips to avoid unsafe situations.
Here's one of my favorites:
When you are in a crossing situation with another boat that's too far away to judge easily, you can easily tell if the the other boat will pass in front of you, pass behind you, or if you are on a collision course, by looking at the shore in the background of the other boat.
If the other boat appears to moving backward, relative to the shore, it will pass behind you. If you speed up or turn away from the boat, just a little, you will open the gap and create a safer crossing situation.
If the other boat is moving forward, relative to the shore, it will pass ahead of you. If you slow down or turn toward the other boat, just a little, you will open the gap and create a safer crossing situation.
If the other boat remains stationary, relative to the shore, you are on a collision course and if you are the give-way boat, you should make obvious course or speed adjustments. If you are the stand-on boat, you need to maintain course and speed unless the other boat forces you otherwise.
Edited to add some crappy diagrams:
This is an overhead diagram of what I am trying to describe:
The yellow block is an object on the shore. The blue line is the sight line between the two boats.
This is a view from the boat in the first diagram, looking starboard, toward the boat near shore, and the yellow object on the shore:
If the boat in the distance appears to be moving forward, relative to the yellow object on shore (the red arrow), the boat will pass in front of you. Slow down or turn to starboard to increase the passing clearance between the boats.
If the boat in the distance appears to be moving backward, relative to the yellow object on shore (the blue arrow), the boat will pass behind you. Speed up, or turn to port to increase the passing clearance between the boats.
If the boat in the distance appears to be stationary, relative to the object on shore, the two boats are on a collision course and crossing situation rules must be followed.