What brand is the kit. You say it has sheet balsa sides? With stringers and formers on the top and bottom? If so, whether you cover the sides over the sheet balsa is optional. You can just cover the top and bottom, extending the covering around the edge of the sheet for about a sixteenth or an eighth of an inch. You can cover the sides if you want with a seperate sheet of tissue. If so, you do not use glue- you use clear dope. Paint the side with one coat of clear dope, immediately lay down a sheet of tissue cut to size, and brush on a second coat of dope. The dope will soak through the tissue and connect with the dope already hardening on the wood. Immediately smooth out any wrinkles. When I cover a fuselage on a model with sheet sides like that, I cover the sides first, then the top and bottom.
If the model does not have sheet sides, I still cover sides first, top and bottom later. Depending on the curves and bumps, you may want to cover tops and bottoms with several pieces of tissue each. the smaller the pieces you use, the easier it gets.
Also, when gluing, put the glue on the wood, not the tissue. Whether using white glue or dope, I use a paint brush to apply the glue or dope to the wood.
There is also a technique, called wet covering, where you slightly wet with water each piece of tissue just before you put it down on framework. I suggest you put this off until you get a few planes under your belt using the tissue dry. The wet tissue shrinks up better than dry, avoiding wrinkles, but is a messy, somewhat tricky job. The wet tissue tears very easily.