The easiest way to get quality sound without having to spend the effort on editing is to use a better microphone and better recording environment, but that's not the cheapest thing to do.
In Audacity, there is an effect called Noise Reduction Select an area of silence/background noise and run the effect to click "Get Noise Profile". Then select the entire recording, run the effect again, and select OK.
I dunno what else you could do other than apply a high-pass filter to remove muddy sounds below 100 hz