 4.15.20  4:45 am   To try to answer this person's question...and you can determine if this is a good way, Bill...  What I often do is that I examine what the highest note of song is or the lead (vocal) melody. Then I let that be the high part of my range I know I can hit pretty comfortably. And then see what key that would make the song in. And then I might move the key up or down depending on what feels good.  Does this sound like a good technique, Bill? That's what I've been using for years and it has worked for me.
of course, i do that too, and that's the most sensible thing in your situation, but from the way i interpreted the person's question it sounded like they hadn't started writing the song yet