Telling somebody that they are doing a good job for every last small little thing is rather condescending. That's generally how you train a dog, not a child. If I followed you around in the morning and said things like:
Good job brushing your teeth, I knew you could do it, good job.
Good job putting on deodorant, I knew you could do it, good job.
Good job getting dressed, I knew you could do it, good job.
Good job eating breakfast, I knew you could do it, good job.
Good job getting in the car, I knew you could do it, good job.
etc.
You would get tired of that fairly quickly, wouldn't you. When you congratulate somebody on every last little thing, the praise itself losses all value, and becomes more condescending then appreciated. Telling him good job after he has completed a task such as finishing his work is fine. But try not to congratulating for everything and anything because doing that just cheapens the whole verbal praise system.