I often struggle with this too. I would be able to sing it ok privately but when it comes time to sing with lots of people around me, the key would turn out to be too high some of the times.

I usually use the rule that people normal range is from C note to the next C octave and adjust songs so that the lowest range and highest range falls in that range. It usually works. But not all the time. I also try to sing the song mentally going through the whole range of notes instead of using the voice and that seems to work a lot too and getting that "sweet" key better. Then trying it with the voice afterward.

anyone else ?