Clamping is more challenging when the glue acts like a lubricant, which it does until it begins to set. Here’s a simple way to get more traction: I put a few grains of coarse salt or sand onto one of the mating surfaces of the joint after I’ve spread the glue. It takes very little grit to do the job. The salt or sand bites into the wood when you apply clamping pressure, preventing the parts from slipping. Sprinkle the grit toward the center of the joint for best success.
– Charles Mak