Here's what I did when I started out.
10 seconds at whatever aperture and whatever size. Printed it, developed it, and looked at it. Too dark? Expose less. Too light? Expose more. It's actually that simple.
In little while, you'll be able to guess a little better.
If this is your very first time, I wouldn't worry about making good prints with least waste. You'll waste plenty no matter what you do....