Half-Lap - As with dovetails, cut one piece first. It isn't critical that the rabbet or dado be exactly half the thickness of the piece, because you will use the cut piece as the gauge to mark for the mating piece. Remember to lay the reference faces (the ones that must be flush when finished) against the bench when marking, especially if you are lapping pieces of different thickness.
Keep the reference faces against the table
Face or Picture Frame Miters - The key to tight fitting face miters is to make the opposing sides of the rectangle exactly the same length. Use the item being framed to determine the height and width of the frame, rough cut your pieces slightly longer than the outside dimension of the frame. Then, stack the two opposing pieces, align the ends and miter cut one end. Now re-orient the pieces to prepare for mitering the other end. Align the previously cut ends so that they are perfectly flush, and you can't feel any misalignment when you brush your fingertip over the ends. Now cut the opposite end, and repeat the process on to the other two sides.
Align by feel, not sight
… and hold to mark