Taildragger... with the aircraft level attitude (as if flying) the axle for the mainwheels should be approximately under the leading edge of the wing. That is a good reference to start.

Many low-wing taildraggers (such as the 4*) the mains are ahead of the leading edge by up to 1/3 the distance that the CG is behind the leading edge, and that's pushing the forward limit. (if the plane is "squirrly" on the ground, put a wedge between the dural and the fuselage and that will move the axles to the rear and help out) I wedged my 4*40's mains 1/8 inch at the front and its much nicer on the ground now.

Trike gear... the mains should never be behind the trailing edge of the wing. Usually 1/2 way to (or a bit more to the rear) between CG and the trailing edge works out correctly.

If a trike plane refuses to rotate, lengthen the nose strut 1/8 inch at a time until the problem's solved.

For most models... the nosewheel should be mounted to the firewall... further back can cause "pogo-stick" landings... where you can't prevent a small bounce from resultinng in the nose jumping higher each bounce... results in the nose getting ripped off the plane almost every landing.