I usually go with an o \/ O looking spread with the "o" being mallards and teal and the "\/" being bluebills and ringbills. I try to put the blocks out as randomly spaced a possible and make sure they're tied so they don't all face the same direction in wind or current. Also, I am compeled by superstition to put only odd numbers of decoys in any line or group. Keep the wind at your back.