What factors or criteria describe best advertising sales contacts programs?

We solicit and receive advertisements from first party adverisers and from advertising agencies. This field is not one I formally learned.

Before considering specific packages I want to learn what best practices or criteria should we hold as primary rules for making our choices?

For now, I have only a passing interest in names of specific applications. If you know any, name the package and web site. I do not want any push on purchasing; please no sales pitches.