And going on from Elmo, keep board flat on the water especially when going broad in flat water. That is, don't dig the tail in or rail the board at all. Keep sail as upright as possible, use longer harness lines than you would say on a slalom or wave setup and you want to imagine the sail power coming through your front hand, traveling through your body and driving through your front foot. The back foot should be neutral and flat and almost pulling upwards but don't over bend at the knee. Sounds strange but seems to work for me at the moment.
One last thing - keep trying new things but only change a little at a time, assess and then adopt or discard changes. Everyone is different so you have to work some things out yourself. Enjoy!