It really depends on the type and size of the bait, wood used, and desired buoyancy. ie, floating, sinking, or suspending. The best way that I've found to do it is by sticking split shot onto a a non weighted blank and moving them around during testing. You can use a small drop of silicon, rubber cement, or tape so that they are able to be taken off and re applied.
As an example, on most of my 3" and under floating cedar cranks, I have found that a single 1/8 oz. or 2 smaller weights placed in front and back of the front hook is all that's needed for ballast. Larger bodied lures such as big musky baits can require more weight spread out across the length of the belly. Heavier hardwood bodies can be made without internal weighting, where the hardware acts as the ballast.
As a general rule, the balancing point on most smaller 2 hook baits will be at or very near the front hook hanger. It's a trial and error process, but you will learn pretty quickly where and how much weight to add for a given type, size, and action of bait that you are building. Hope this helps!