First and foremost: More complex airplane means more things to think about - don't foreget to fly the plane first and always. Everything else will wait for you to keep the aircraft in safe flight. If you're exceeding your total capability, go back to a simpler plane!
Have a mind for more precise anticipation of speeds. The 172RG is pretty forgiving, but you'll still want to plan to fly the aircraft so as to slow down (without slamming the throttle closed, and shock cooling the engine) so that you can enter the circiut at a speed such that extension of the gear and flaps does not require areobatics for speed management. Plan well ahead. This is much more applicable to slinky high performance types, which are hard to slow down, but equally valuable to practice in the 172RG.
Also remind yourself that in single Cessna RG's the pilot has a first hand view with which to confirm the extension of the main gear, but not so much the nose. This has two important aspects: If the nose gear has not extended, you may be distracted into thinking it has because of the thump, and presence of the mains. If you are conducting a forced landing, and you go through the checklist too quickly, or wrong order, you can get the gear on the way down, and actually get the master off (as a checklist item) before the nose gear is down. The result can be landing on the mains, and partially extended nosewheel. It's been done many times. Look to see if there is a mirror in which you can see the nosewheel. When flying at night, it can be useful to recall what the profile of the fuselage looks like in the mirror, so you can fly some lights on the ground behind the nosewheel, to see if you get the desired "nosewheel eclipse".
It will probably have a landing gear selector which you have to pull out to move. Pull on it to move it, don't force it (if you break off the knob, you will wish you hadn't later).
Confirm by visual inspection of the selector knob position, that the landing gear is selected down, before you turn on the master on the ground for any reason (pre flight inspection). The "WOW" weight on wheels switch is on the nosewheel only. If it is U/S, and someone left the selector up, the nose wheel is going to retract right then (it will go much faster than usual, 'cause the mains are not moving). If you have people in the back, and a load of baggage, and the nose wheel is light, it could also retract even with a working, but poorly rigged WOW switch.
When you switch the master on, you will probably hear the pump run for a few seconds. As long as it shuts off promptly, that's fine.
Also begin to consider those circumstances where landing with the gear up would be preferable- there are some.
There are lots of other things you will learn as you go, and the advice here will be a good part of that. It's just mind expanding, and in aviation, that's always good!