How deep to run your baits often depends on how deep the fish are. Watch your electronics carefully to get an idea of where the bait and fish are in the water column. Many times you’ll see a congregation of activity between 17′ and 22′ down. You’ll also see another near the bottom.
I try to target these two zones (bring a freind so you can run two lines), and be as specific as I can with my depth. Depending on the day you may get fish in both zones, or only one of them. If only one is hot, check to see if your running a similar bait at both depths. If not, try it. If you are and only one is going, try something different at the other depth. For example, let’s say I’m pulling perch colored baits and getting bit on the bottom hugger, but not the high bait. Could be I need a bait that will mimic the prey that is up higher, say a tullibee/cisco color combo. Might work, might not, but it’s worth a try.
As to the depth issue I’d encourage you to get a trollers bible. There are different ones available that will tell you exactly how deep your bait will run. There are some deep divers that can hug 32′ of water. Others may only get down 20′.
Good luck and maybe we’ll see you on the water this weekend.