The basic principle of mast rake is the further forward the mast is angled the more power the boat will develop, however this is a trade off as the further back the rig is raked the closer to the wind the boat will go. To set up the mast rake correctly I would first suggest that a neutral position was found (dead upright) this can be achieved by positioning the pin in the mast step towards the middle and adjusting the shrouds so that when the jib is on and rig tension is on the mast is upright.
If you feel you have weather helm (boat continues to round up when sailed flat, move the mast forward at the step, if you have lee helm move the mast back in the step. This changes the point the boat pivots around.
Once the trim is set then I would look at the mast rake to get the ensure I had good pointing ability and good power. This is a trade off and in more complex boats the whole rig will tip forward and back depending on the leg of the course being sailed.
I hope that is of some help setting your boat up!