When fishing in the summer, it pays off big time to find the cooler spots in the lake. The temp. sensor on your depth finder should do that for you. I fish on lake Sam Rayburn and during the summer i like to use spinnerbaits and soft plastics.
Another good technique for summer fishin is flippin and pitchin surface slop. A lot of times the fish will get up under the slop to escape the heat and hide in the shade. They will also hide under lilly pads and any other thing that will provide shade. Hope I helped you out a little, good luck!