Maximize the chilling water flow and leave it there. Slow down the wort flow until your target temp is met. Of course, the wort output wont get below the temp of the chilling water.
Make sure the wort is entering on the OPPOSITE side as the chilling water. This is why a plate chiller is called a counterflow chiller: the two fluids need to be going in opposite directions. Occasionally, when I am in a hurry, I hook them up going in the same direction and it doesn't cool at all.
Get some cheap quick disconnects. Makes the job much easier. Since you have barbs, you'll have to connect a stub of tubing, then the quick disconnect. Hold the tubing onto the barbing with cable tie or hose clamp.