Sometimes you need to cut a tall fuselage side from several small pieces of wood. Or maybe you want to build a fully sheeted wing that requires two or more sheets to be joined. The first thing to do is to assure that the two edges to be joined are square and able to come together without gaps.
Once you have a well fitted joint, you can simply lay the parts flat on the table, hold the joint tightly together, and apply thin CA glue. This works, and I have done it many times myself, but it makes a hard, lumpy joint that is frequently visible through the covering.
A better way to create an edge joint is to use Titebond, white glue, or any carpenter’s glue from the hardware store. You can also use traditional nitrocellulose cement, which used to be a common product called Ambroid. There’s a guy on ebay selling a similar product that he calls Ambrulose. You can also use Sig-Ment, or you can buy a can of Fab Tac nitrocellulose cement from Aircraft Spruce.
First, assure yourself that the joint is tight. Sometimes the two sheets are not the same thickness, which will create a step in the joint. You can sand the thick piece to make an even joint, or if the difference is only slight you can ignore it and make sure that the uneven side is placed toward the inside of the plane.
Hold the parts tightly to the table, and hold the joint together tightly. Apply masking tape. It doesn’t have to be one long piece. You can use several shorter pieces if you like.
To avoid trouble later with paired parts such as fuselage sides, tape the joints on opposite sides. This way, if you have a smooth side and an uneven side, you can put the smooth side out on both sides of the fuselage.
Turn the pieces over and fold the joint back to expose the adjoining edges. Apply glue sparingly with a toothpick or other small tool. You don’t want big gobs of glue to squeeze out. Use just enough to make the parts stick. 
After applying the glue, place the part on a flat table, tape side down, and hold it flat with heavy objects until the glue sets.
