As for cruising altitude for a C-172, pick an altitude that will clear the terrain (especially over populated areas) by at least 1,000 feet (you can climb and descend, if you wish, as the terrain changes). A sectional chart is usually the source for this information over most routes. With a C-172 you probably will be most comfortable at or below 9,500 feet, but there's nothing stopping you from climbing to the service ceiling of the aircraft if you wish. For climb you'll often want full power (leaned above 2K-3K ft of alt. MSL), and perhaps 90-95 kts IAS near sea level (less at higher altitudes, since climb performance is reduced up there) or so, though (for engine cooling) I'd not go much below 80 kts IAS or so except when very high and performance is nil.
You'll want to consider the east/west altitude rules (at and above 3,000 AGL):
(1) On a magnetic
course (not heading) of zero degrees through 179 degrees, any odd thousand foot MSL altitude + 500 feet (such as 3,500, 5,500, or 7,500); or
(2) On a magnetic
course (not heading) of 180 degrees through 359 degrees, any even thousand foot MSL altitude + 500 feet (such as 4,500, 6,500, or 8,500).
Cruising airspeed is whatever you like, up to 75% power during cruise, being sure to lean the mixture after leveling off if you're much over about 3,000 feet, or so. Often 2300-2500 RPM is used (lower RPM is quieter and, with no wind or a tailwind, a bit more fuel efficient). Note that TAS for a given altitude and power setting (along with fuel burn) are in the performance section of the POH. Typical rates of climb and descent are around 500 fpm, or so, partly for aircraft performance but partly for considering changes in pressure that can affect people's ears as the ears pop (or don't).
Of course you have to figure time and fuel requirements for the trip (unless you run unlimited fuel in the sim), which means you must figure how far the trip is, how much of that is climbing, how much is descending and how much is cruising (fuel burn rate and (usually) speed are different for each of these), and of course winds must be considered (I'd suggest no wind 'til you get used to it).
When planning, you'll also need to consider magnetic variation through various parts of the trip (for plotting the course), along with variations in winds aloft. And if using the GPS, you can (usually) go in a straight line if you wish (IRL certain airspace types must be avoided or dealt with), while if you are using VORs and/or NDBs you must use charts to plot the course lines between departure, VORs and destination, which will affect distance, since it's rarely a straight line.
There's a lot more, but I've given you quite a bit to think about (use as much or as little as you like, or ask more questions), but I'd also like to point you to the FAA's web site where the
Pilot's Handbook Of Aeronautical Knowledge (PHAK) has a LOT of good information, with Chapter 16 being about Navigation:
https://www.faa.gov/regulations_poli..._phak_ch16.pdf
So being in a sim you can choose as much or as little of the above as you like. Luck...
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