Everyone knows the basic “dos and don’ts” of the commode: don’t flush any kind of paper other than toilet paper, if a commode starts to back up you can shut off the water by turning the knob at the back of the commode near the floor – righty tighty, lefty loosey.
There are a couple other things to keep an eye on, or an ear out for: see if you can rock the commode back and forth or front to back. If so, you should tighten down the bolts. There are typically two bolts fastening the commode to the floor, which are usually covered by plastic knobs. Do not tighten bolts too tight as you can crack the commode.
If your commode sounds like it is constantly running you might need to have a plumber replace the fill valve. You can also take the cover off the back of the commode and see if the refill tube goes down into the overflow tube – it should actually hang just above it. If that is not the case, you can try adjusting the ballcock or float cup lower and see if that fixes the problem.