I have never fished Cooper. However I would get an early start before it gets to hot.
Fish around docks and overhanging tree limbs.
Also fish the edges of grass beds. I would use live worms for bait. The Sunnies down here are usually pretty active between 7am and 11am.
Once it gets hot the Gills will still bite but they also tend to get lazy and are not as active.
Good luck and let us know how you do.