Sweep strokes, low braces, and draw strokes are the most important. The latter are critical during rescue situations. When performing paddle strokes like braces, sweeps and draws, most of us have a preferred side and an 'off' side. If you practice only on your 'on' side, you will get better but only on that side. But the discrepancy between the two sides will only increase.
Navigation is another example of skills progression.
First, learn to estimate your speed in a variety of conditions. Do this by timing yourself paddling a known distance, then calculate your speed. This skill is essential during crossings, so be sure to master it beforehand. Practice listening to marine weather reports. The best practice is to record what they're saying.