Vessel movements at sea are governed by the internationally agreed Collision Regulations 1. These also apply on most inland freight waterways.
While the rules about avoiding collisions are fairly simple on more inland freight waterways (keep to the right to avoid collisions, unless signalled to do otherwise), you need to be slightly more familiar with the rules if you are entering larger estuarial waterways.
The main point to understand is that the rules require you to alter course to starboard when you are on a collision course with another vessel (Rule 14). If the course of both vessels is such that there is no danger of collision, do not expect the other vessel to alter course so as to ‘keep right’. The rules also explain which vessel gives way in a crossing situation (the vessel which has the other on her starboard side must give way – Rule 15).
On canal and river waterways, vessels should keep as far to the right as is safe and practicable (Rule 9). Be aware however that a large vessel may need to move across the waterway frequently to find the deep water and you should communicate by radio or take note of sound signals, in case a ship coming the other way wishes to pass you on the ‘wrong side’, i.e. by keeping to the port (left) side of the channel. Note that pilots and vessel skippers will often refer on the radio to passing ‘red to red’ (the normal situation where you are both keeping to the right and pass port side to port side) or ‘green to green’ (where you both keep left and pass starboard to starboard).
The COLREGS also stipulate lights to be carried – see the next section. As well as making sure you have the correct lights, you should also learn to recognise other light combinations, for example as carried by a tug and barges. Keep a suitable reference booklet handy if you are moving at night or in poor visibility.