What I was taught back in the day (*rolls eyes*) VG = Vapor, PG = Throat Hit and better flavor.... the correct mixture is extremely subjective like flavo(u)r preference.
I experimented with mixing the first time i was a vaper and I learned that VG/PG ratio takes a lot of personal tinkering. Try it out like you're in a lab as long as you're not stupid enough to screw up the mg/ml nicotine mixture you're golden (Which I would sincerely hope no one who mixes themselves is dumb enough, but the disclaimer is warranted).
another thing to consider is the volume of your flavoring and nicotine which can a be PG base. so yes indeed, it does take a lot of tinkering, cyphering and blood, sweat and tears.