To ensure the tightest of gaps between each balsa strip I rub over each edge with a small sanding block and 120 grit paper. The first edge which will be the open edge is sanded at 90 degrees, then I turn the strip over and sand the edge that will be glued at a slight chamfer. The angle of the chamfer normally increases towards the bow and stern to ensure a good gap free joint.
I have also found out that using the glue sparsely is the best way to reduce sanding and also vastly reduces the grab time. If you think about it you don't need a lot of glue to adhere 1/8 or 3mm thick strips of balsa together. Trust me sanding large globules of glue run off from inside a hull is a thankless chore.
Over time the hull slowly evolves. With this particular IOM I'm restricting myself to two strips on each side before leaving it alone for a couple of hours for the glue to cure. Whilst this is happening I add a couple of rubber bands and perhaps temporary wedges just keep everything nice and snug.