The POH actually contains very sensible advice plus a practical method on this. Did you read that?
The other methods I've heard were (all based on full tanks):
Fly half an hour one tank, then switch tanks every hour.
Fly on left tank if the big hand on your watch is on the left side of the dial, right tank right side.
Me personally, I just incorporate things in my FREDA check and fly on the fullest tank all the time. But I'm not making trips to the limit of the endurance in a PA28. Oh, and if I have a weight inbalance in the aircraft (flying solo or with a real heavy bloke in the RHS) I try to compensate for that with fuel management, for what it's worth. Not sure if it actually makes a difference though.