Though this will have the most immediate benefit, it seems to be practiced only by a few in our sport. Facets of this effort consist of reading about sailing and applying what you read to the operation of your boat. It doesn't matter that the book was written for some fellow who has to sit in his boat. The physics of air and water, and the forces that make a square-rigger go, are the same ones that will push your boat across the finish line. The monthly literature is full of good articles. There is so much information that I've taken to a filing system that organizes the different articles that appear. Now, when I want to find out what the pundits have to say about "downwind sailing", I just open a folder and 10 to 15 articles fall out in my lap.
While you are reading, take the time to learn the proper nomenclature for the parts of your vessel. A clew is a clew. A clevis is not a clew, nor should either be called a "thingy, do-jigger, of thing-a-ma-bob". If you don't know the proper names, when somebody tries to help you, it will go in one ear and out the other. Learn port from starboard, upwind, leeward, and so on.
More information can be obtained by talking to others. By others, I don't mean theoreticians who are great at the blackboard but in the back of the pack on the course. Very often, there will be no apparent explanation why some adjustment or other makes a boat go faster. Don't worry about that, if red jibs make boats faster… go get a red jib!! Get fast first!! Worry about why you are faster later on. A classic example of this occurred in our EC/12 fleet. One boat carried an unbelievable loose jib sheet, yet his boat pointed a great deal higher that the rest of the fleet. I took a couple of measurements, set my boat up exactly as his, and presto, pointed right with him. It was somewhat later that we discovered that the pointing was the result of a fairly tight main leech. The loose jib allowed the boat to come up under the influence of the main, while a tighter jib would have held the head of the boat off the wind. What is important here is that by duplicating his set up, I got an immediate improvement in my boat. Your quest is to find out what is working for the winners, not primarily "WHY". The "WHY" will come as a natural product of your reading and experience.
Observe other skippers' boats. All too often, I see skippers paying no attention to the heats that are sailed without them. These are just the moments that you can give full attention to learning what the winners are doing right, as well as what the losers are doing wrong. We have an advantage over big boat skippers, since we are able to see our hull and sails as a functioning entity. Poorly trimmed sails, too much heeling of the hull, erratic steering, and so on, are ours to see and learn from. Comparison of our boat with the competition allows us to make immediate changes to improve performance. I might add that how the boat is handled is just as important as the physical set-up of the beast. The hand on the transmitter makes a dead boat come alive. If you don't believe it, put the last place boat in your fleet in the hands of last year's champion. By the end of the day, he will be winning his share with it. At the same time, his going machine will have slunk into last place under the heavy hand on tail-end Charlie.
Learn your own boat. Take the off weekends to put her on her side with the rig up. Tighten the backstay, tweak the shrouds. Which the sails in and see if the sheet tension is distorting the mast. Now flip her over and see if it is symmetrical on each side. If not, you may well be on your way to discovering why she goes well on one tack. Check the internal stowage. If you have a battery that goes clunk from one side to the other as you tack, it may be funny…. But it is costing you precious stability, and must be remedied.