Find the constraint
Every sport is a contest against a limit: gravity, water resistance, an opponent, a clock. Working out which limit is binding tells you what the athletes are optimising and makes their choices legible. You can usually spot it within a couple of minutes, long before you understand the scoring.
Use the best as a reference
Watch whoever is clearly excellent and note what looks different: less wasted motion, better position, earlier preparation. Then use that as a template for everyone else. Comparison teaches technique far faster than description does, and it works even when the commentary assumes knowledge you do not have.
Leave the rules for later
Detailed rules are the last thing worth learning, not the first. They explain edge cases, and edge cases are meaningless until the ordinary case makes sense. Anyone who tells you to read the regulations before watching has forgotten how they learned their own favourite sport.