1) Probably the two most important strings on the boat are the backstay and the jib outhaul. The backstay allows you to control the power in the main. More backstay tension will yield a flatter and therefore less powerful main. If you have helm Pull in on the backstay! The jib outhaul allows you to control the twist of the jib and therefore the slot between the main and the jib.
2) Never sail the boat upwind with the traveler centered. It should always be between 1/2 and 2/3 of the way down. In lighter air it should be 2/3 down and the mainsheet relatively tighter in order to get the force vectors facing as far forward as possible.
3) The aft end of the jib boom should never be inside the edge of the cabin top. If it is, you are guaranteed to sail slow. The slot needs to stay open to promote good air flow between the main and the jib. If you are carrying a big bubble in the main it could be because the main is too full, but more likely it is because you have the jib boom too far inboard and/or are carrying too much tension on the jib outhaul, thereby preventing the jib leach from twisting.
Ralf Morgan, Hull # 272