I'll echo most of the other comments. The two primary issues when transitioning from a CE-172 to a PA-28 are the view during landing and fuel management.
The PA-28 series tend to land flatter than the equivalent Cessna. Depending on seat position, for most of us the proper touchdown position is with the nose covering the end of the runway. In a Piper, you will still be able to see the runway in front of you.
Hint for all transitions to new tricycle airplanes: notice the position of the nose when the mains first leave the ground on takeoff. That's the view you want when landing it.
The other issue is fuel management. Because of the low fuel tanks, gravity feed no longer cuts it, so you need to use the auxiliary fuel pump for takeoff, landing, when switching tanks, and most maneuvers (like slow flight and steep turns). Every time you flip that fuel pump switch on or off, it should be accompanied by looking at the fuel flow gauge to confirm everything is working properly.
And, of course, you'll have to switch tanks periodically. I also use the analog watch method - big hand on the watch points to the tank in use.