First, You'll need a standard, 8.5 * 11 inch paper.
Fold the paper so that you have a 45 degree angle.
Copy on the opposite side, then flip your paper over.
Fold the paper like shown in the image.
Press down, and fold the top right flap into the center. Copy on the opposite side.
Fold your paper in half, so that the previous folds are on the outside bottom. (my photo has the plane standing upright)
Fold the wings down, about an inch, while also folding the second-last folds.
Fold the wing down on the opposite side, like you did the first one.
Flip over your plane.
Fold your bottom folds out, in any way you like. :)
Here's what your finished x-wing should look like (if you folded it the same way as me)