Integrating different strokes together into one fluid movement.
The importance of connection to your kayak, so that your movements are its movements, and when it moves, you feel the movement and can react accordingly.
The key strokes that make a paddler amazing are the simple skills diamond. Low/high brace, Forward stroke, Sweep stroke - simple strokes taken to the next level by good edging.
This is a video I found on youtube via reddit - I think - of a paddler in a tide race in Victoria BC. He perfectly exemplifies the concepts above. He flows smoothly between different strokes, braces, forward strokes, and stern rudders as he moves from trough to peak of each wave. Truly beautiful to watch - the slow motion helps, but I am sure it is beautiful to watch at regular speed as well.