Do the fish tend to hang out on the tops or bottoms of the flats at certain times of day, or is it more random?
General rule of thumb is low light periods, early morning and evening they should be on the top side. As the daylight progresses they tend to slide off and will be on the bottom side or the outside edges. That is generally speaking, the BEST thing you can do is drive around the flat and mark them on the electronics, if you see numerous fish on the top side those will most likely be feeding fish, if they are all on the outside or bottom side of the flat, those are going to generally be a little more negative, they usually move up to the top side for one reason and that is to feed. That does not mean you will not catch any when they are on the outside edges or bottom side of the flat, but if you mark them up top, they should be more aggressive. If you see them tight to the bottom anywhere, those will also be a little more negative than fish that are sitting a foot or more off the bottom. I would not fish a flat unless you mark them first and not just one fish, you should see pods or groups of fish, those are the ones to start with, look for inside turns on the flats and the steeper breaks as your target areas, also wind plays a difference, fish the side the wind is blowing into it. As mentioned before, Mille Lacs is a long snell lake due to water clarity. 6′ snell should be minimum. Prince Bait has a good supply of pre made 9′ snells. Color will make a difference as well, but this year has not been as critical. If you have a couple people in the boat, start with 3 different color combinations, bright, dark and shiny. Once you pick up a couple on one color, then change the other ones out to something similar color and you should have a pattern.