In this video with Mat Hines from iZotope, he covers some basic recording tips and then shows what some of the common audio problems look like on a spectrogram and how they can be fixed with editors like izotope's RX audio repair toolkit.

If you haven't got your head round what iZotope RX can do then this is a helpful little video which should help you be able to visualise the issues and then see how you can resolve them in RX.

If you haven't got iZotope RX5 then you can download a 10 day free trial from the RX page on the iZotope web site.