In theory you want to get the centre of effort of the rig (wind pressure) over, or with a very slight lead over, the Centre of Lateral Resistance of the hull. To find the latter, you put the hull in the bath weighted down to the waterline and push it sideways with one finger. The point at which you push it so it moves sideways without slewing to bow or stern is the CLR. However, the rudder affords some lateral resistance so you need to dummy one up before trying the experiment. If you then want to fit a drop keel and keep the CLR the same, the centre of effort of the keel (dropped) will need to be in line with the CLR. Height of mast -say about 1.5 times overall length of hull?
That's just for starters - now the experts can have a go!