To do a tissue and dope job on a wing, lightly paint all the edges of the wing with a thin coat of butyrate dope and let it dry. Then spread the DRY tissue over the under-surface and lightly brush more dope along the leading edge to get the tissue to stick. Then pull the tissue flat and paint only the trailing edge and whatever portions you need to wet of the wing tip area. When the dope is dry, use some fine sandpaper and lightly sand the edges to remove the overhanging edges of tissue. This produces a "feathered" edge to the tissue that will disappear later. Tissue will shrink as it dries to a size smaller than the dry material originally was.
Now do the same thing on the upper surface of the wing, including gently sanding the edge to remove the excess tissue.
When you are ready to coat the wing, brush the dope on the under-surface of the wing, but be sure to keep that surface DOWN as much as possible. The dope will soak through the tissue and collect on the lowest surface, and you want that surface to be the outside to minimize the amount of dope needed. Apply just one coat.
Now coat the upper surface of the wing, but turn the wing upside-down so that surface is always facing earthward. One coat only.
After it dries, you may need to apply another coat to the wing, but again do the bottom surface first, then the top.

If you were covering the wing with Silkspan, you would do so with the material wetted with a mist sprayer, because Silkspan stretches when wet and re-shrinks as it dries to the original size.

And make sure you have good ventilation.