Like most people I start out with zero/zero then fly the plane. At the field I just use washers to add the thrust if needed. When I get home I then make up a beveled thrust plate from ply and it goes behind the motor mount. Each plane is different so it's just part of how you trim. Most planes end up with a bit of right thrust and some want some down? You never really know until you fly the plane. Some kits and ARFs put the thrust they figure is best after a lot of flight testing and it's often very close.