Step 1: Materials
Hardware: Clamps, Straight edge (ruler), box cutter
Paper or plastic to place under posters to catch any glue overspray
Step 2: Apply Glue!
Step 3: Stick them!
Step 4: Trim!
A clamp on each end and a steady hand guiding the blade along the straight edge made this pretty easy. Of couse a good sharp blade helps, especially with thicker boards... you may have to make a few passes with the blade.