Nothing teaches you to sail better than just messing around in a small sailing dinghy. This puts you in touch with the boat, sails, wind and water, and the best thing is you don't have a back up motor so you quickly become reliant on gaining sailing skills. You will gain an understanding of all the forces involved in a way which you would not learn on a large boat. The skills you acquire in the small boat can then be easily transferred to a larger yacht.
No one taught me to sail, I never had lessons. As a child my first yacht was the family dinghy on which I put a square sail rig, and made a rudder. I then went on to a Sabot sailing dinghy and had great adventures as a child sailing around our nearby coastal waters. The skills learned then are the same that I use now. Seamanship, which is something a little different, is learned by experience and the application of good judgement.