For very rudimentary flight planning purposes, you could assume the plane has a range of about 500nm, although there are many other factors at play here.
Endurance is the key factor: figure out the speed you want to fly at (if you're going somewhere, you'll probably want to cruise at 70-75% power) and calculate your endurance (48 gallons usable fuel, 8-9 gallons per hour).
Let's say it's about 5 hours (overesimate fuel burn and round down endurance times).
Give yourself at least an hour's buffer of fuel (and possibly more to ensure you can reach a suitable diversion plus have a comfortable buffer on top of that - this will depend on your destination). Add a further 20 mins to deal with startup, taxi and the extra fuel you'll burn during takeoff and climb.
That leaves you with about 3:40 of time to fly. At 75% power (110kts), that should give you a rough figure of about 400nm.
Then factor in the winds and the effect they will have on your groundspeed. Always overestimate a headwind and underestimate a tailwind and remember that crosswinds will have an effect too.
Remember to lean properly as the fuel burns in the POH will almost always assume proper leaning technique (level flight, stabilise airspeed, set power, slowly reduce mixture until you sense engine roughness and then push the mixture lever forward about an inch - remember to enrichen for climbs and re-lean every time you change height).
You'll also want to think about yourself and your passengers - I find that anything much about 2-2.5 hours in a light single in one go starts to get uncomfortable. If you have passengers, will weight and balance allow you to take full fuel?
Few things to think about, a lot of variables, but that's why pilots are special.
The legal bit: everything I have written is qualified entirely by the aircraft's POH.