If you are just using a topo map, then look for drop offs to start with. Drill a line of holes from shallow into deep water. Maybe 10 holes, 20 feet apart. Fish each hole for 5-10 minutes until you get hits. I am currently fishing in 40-70 feet of water at all times of the day.
I use a colored sonar (and recommend it), and I move constantly until I find fish. Although perch are considered a schooling fish, I will pick up individual fish with long periods between fish. On the sonar, you can see single fish come in to the bait, and no bites, then the next one will take.
If you get in to a school, then they are much more eager to bite. I have returned to previously fished holes and thought my sonar was broken, only to realize there was sixteen feet of fish flashing on the screen. When I hit a school, the action is fast with immediate strikes once I reach depth.
Keeping on top of the school is difficult. Drill 50 yards away in each direction, and see which way the school is heading. This is, of course, much easier with the sonar. After that, you may be able to jump ahead of the school, but they will move in a circular pattern, which complicates things.
In short, whether using a map or a sonar, be mobile. If the fish quit biting or aren't biting, move.