One quick and easy way to “level or normalize” your wav file is to drag and drop it onto “Levelator.”
It’s a free download and seems to work fairly well.
Unfortunately, it doesn’t work with mp3 files.
This assumes your audio is pretty good in the first place.
The old rule of GIGO – Garbage In Garbage Out applies.
If you have a lot of background noise you may want to use a real audio editor to get rid of that first before you try Levelator. Audacity is a FREE editor which works pretty well.