Read the wind. Time your start. Race a fleet that knows the rules. SailMOB is a racing-physics simulator that teaches you to sail by sailing, from your first tack to the tactics that decide a regatta. Free. No boat required.
No download. No credit card. Runs in your browser.
Port and starboard, mark-room, windward-leeward, penalty turns. The full RRS Part 2, and the whole fleet sails by it. Break a rule and you'll know. That's how it sticks.
Hull drag, leeway, polar curves, wind shadows, puffs. Sail it badly and your speed shows it right away. The quickest way to learn what a clean lane is really worth.
Ask why you lost that mark-room call and get an answer from your own race data, not a canned tip. Real coaching on the race you just sailed.