Producing a final master involves playing of instruments, programming, engineering, and organization, but most of all, it requires a great song.
It is my humble opinion that before diving deep into the production process and spending money uselessly, it is very important to evaluate the strength of the song.
I like to record a simple demo, then listen back and evaluate the song’s strengths and weaknesses.
Can the structure be improved?
Can changing key bring out more emotion and help deliver a better vocal performance?
A simple demo strips the song of anything that might distract us from really evaluating the song.
Of course, this is all very subjective, and not suited for all genres. From experience, this most often helps.