Remembering my days teaching Junior club, I'd say for the fastest gains you would want to:
1) Get the best boat (the one with LESS holes/ Problems than other boats)
2) Get the newest sails in the club
3) If you can pick your crew, take a light guy on a light air day and a BIG one for heavy air
4) Set up your boat for success - Put the right amount of draft in your sails, the proper mast rake, and
rig a shute if you can handle it. Get your instructor to help/ check if you've set up boat for conditions.
Again, I'd say those four will give you the most immediate benefit, of course, it's just a starting point.
GOOD LUCK!!!