Keep a lookout at all times for other vessels not just with your eyes but also your ears!
Power gives way to sail
BUT
In a narrow channel ie the approach to any harbour or port, dinghies must keep clear of merchant ships. The bigger ships often need deep water and may not have enough room to get out of the way.
REMEMBER large ships take a long time to alter course to avoid another vessel. Make a bold change to your course in plenty of time for them to see what you are doing.
Just because you have right of way DO NOT ASSUME THAT THE OTHER BOAT WILL MOVE. Keep looking and be ready to move out of the way.