Centreline layout method works extremely well. Identify the faces of your timber. Level the face of the timber where your joinery will be. Layout centrelines on each end. Join your lines on each face with a chalkline. You now have a centreline on each face if required. If your timbers are not say a perfect 8X8 than you can go from the centreline and snap lines to the outside. All joinery layout begins from the centreline. This system makes it easy to deal with irregularities in timbers.
