It is a sad fact that one of the more difficult steps of kayak building occurs right at the start of the project. The sheer strip of a strip built kayak forms the edge of the seam between the deck and hull. To get a tight fit you want to form a mitered edge where the hull will join the deck.
When building a strip planked kayak, I typically start on the hull. I then have one strip that follows the sheer from bow to stern. When using cove and bead strips, I will cut the bead off first. This gives me a square edge. I then place small sticks of wood on the kayak building forms to show the angle of the bevel that I will need.
These sticks serve as a guide for the bevel you will need. I use a block plane of shape the edge of the strip. I look at the gap between the strip and the stick, and hold my plane to match that gap. I then plane away the edge, maintaining the same angle, until the gap disappears. I check my results on the forms and make adjustments as needed before moving on to the next form.