Thinned dope is the classic way to attach tissue. There are other alternatives that some people prefer. A popular way that is pretty easy is to use glue stick. Its very simple to simply spread the glue on the perimeter of the area you are covering. If you want to stretch out wrinkles you can simply moisten the edge and the glue releases again. When you dope it the glue the adhesion is water proof.

As far as dampening the tissue goes, I usually use a spray bottle to mist the tissue. The wetter you make it the more likely the surface is prone to warping, especially wings. Try dampening it a little first. If there are still wrinkles when it drys dampen it some more or pull out the wrinkles by loosening the glue. I have taken to pinning the wing to a flat surface as it drys to avoid warps. Painting temporarily loosens the tissue a little again but usually doesn’t introduce warps.