For precision hand-woodworking, a marking knife is essential. This flat-on-one-side, beveled-on-the-other blade has a variety of uses that will make your wood cuts easier and more accurate.
How thick is your pencil lead? Whatever your answer, I guarantee that the blade of your marking knife is thinner. This can really make a difference for cuts where even 1/16 of an inch will matter. You won’t need to decide which side of the line to cut on. Plus, your knife will cut through the fibers of the wood, instead of wobbling across them like a pencil might.
The first few strokes of the saw are the most important. Line up your cut with an engineer’s square, then drag the marking knife a few times to cut through the fibers to make a V-notch for your saw to rest in. This keeps the saw from jumping or shifting for those first few strokes.
The rule to measure twice and cut once should really be reversed for dovetail joints. You should only be making measurements (or using a template) on the board you plan to cut your tails out of. To create the pins on your other board, use your marking knife to trace the outline before you saw and chip out the waste wood.
Having trouble seeing the line you cut with your knife? Take a pencil and go over the cut, then use an eraser on the flat of the wood. The lead inside your razor-sharp line will remain, making it easier to see.