The main thing you will notice is, if the propeller is fixed pitch, you will have the throttle all the way in to maintain cruise power (9000 ft will limit you to about 65% and the engine will be wound up close to, or at the engine RPM redline, and throttle setting might be limited by redline if the prop is pitched too fine.
The other one is it will be cold and the heater had better be working.
Indicated speeds you use are unchanged, but just be aware that the difference between indicated and true are starting to become significant and your indicated cruising speed will be lower than what you are used to, with less margin between operating speeds and stall (whose indicated airspeed remains the same).
Biggest one is to be aware that your overall energy margin that you get from excess power is declining off to zero as you approach the airplane's service ceiling. If the service ceiling is 12 or 14000 ft, you should still have some energy margin at 9000 ft, but nothing like down low. This applies to maneuvering margins as well; it's easier to stall the thing in a steep turn say.
If you don't have altitude compensating carbs, mixture leaning is an obvious one, but that really applies to all altitudes as soon as you reduce power after takeoff (a full rich mixture is strictly for cylinder cooling at full power, at lower altitudes where full power or close to it is available).
Otherwise, not such a big deal. Don't over-think it. Just learn the facts and keep them in mind.