As an example, I will take my Dime Scale Stearman 76 again, which features a one-piece upper wing, and two lower wings butt-joined to the fuselage sides.
Using a photocopy of the plan, with the correct incidence angle drawn in, a template was cut out, representing the space between the bottom of the upper wing centre section and the top of the fuselage. The position of the wing leading edge was marked by a step, and the positions of the fuselage formers, plus the front of the cockpit noted. The paper cut from the plan was glued to a bit of thin card, then tacked onto the fuselage, along the top stringer, using a couple of dots of PVA.
When dry, the wing was tacked to the top of the template along the centre rib, again with PVA, positioned with the LE at the correct position. To keep the wing level when viewed from the front, a pair of temporary balsa struts were tacked into place, from the lower fuselage to somewhere under the outer wing panels.
You now have a sort of parasol arrangement, which will be rigid enough to stay in place while you add the four centre section struts one at a time. The plan shows 1/16" square balsa for these, but I used cocktail sticks for strength. These had been previously covered in blue tissue, to match the fuselage, and were attached using cyano.
Once the struts were fully set, the jig and temporary supports were removed after softening the PVA with a wet paint brush.
To correctly space the upper and lower wings and set the stagger, another jig was cut out, to slip over the tips of both wings. This also keeps them at the same incidence while the lower wing is glued to the fuselage side. The model must be viewed from above to check the wings are parallel.
The wings will have enough spring in them to allow the later addition of the hard balsa interplane struts, though it is best to slip the jig over the wings again once you have done this to recheck the angle and spacing.
If you are building a model where the lower wing is a one-piece affair that passes under or through the fuselage, then this will be fitted in place before the upper wing. This means the second wing-spacing jig will probably not be needed (though you could still make one to check the relative incidence angles of the wings). In the photo below, my Boeing F4B-2 has its upper wing mounted on a jig, exactly as per the Stearman, but steadied using thin balsa strips connecting it to the previously attached lower wing. Two of the centre section struts had been already added when the picture was taken.
Returning to the Stearman - this was finally rigged with fishing nylon, attached with cyano. This "working rigging" has the effect of strengthening the structure considerably. When the photo below was taken, immediately prior to the first test flights, the rear gun and windshields had yet to be fitted
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