Well I'm no expert and have never fished Grand Lake, but summer fishing here they find "flats".....the gentle slope between the channel and shore....and they dip minnows/jigs/combinations of both around standing trees or sunken brush. Fish very slowly...that is, when you get your bait down to around 10', hold it pretty still for a bit, then maybe a little twitch. If no bite, bring bait up to 8' and try again. You may find fish as shallow as 4-5' , depending on water color, or as deep as the thermocline.
Good luck and welcome to the site