Naturally having a beautiful model present during a light test or a friend during a location scout is ideal, but not always available. You can do a few things... You can walk with a mannequin head to test the light. This is ridiculous but I've seen people do it. You can make certain someone is there with you, but after a few "Hey just stand there for a minute and look at me" statements, they'll grow tired quite rapidly. There's the alternative which is something I use for my work and it's my hand. Yes, my hand and here's now...
As a photographer I'm always looking at light. When I walk into a friend's home, I'll probably compliment the light before the home. It's not that I'm being rude, but I see the light first. When I shop for a new home, I look at the light as much as the location. Lighting is everything and of course, I'm biased but light changes/creates a mood. Invite me in your home or place of work, you'll see me turning my head in every direction. People that don't know me describe the process as "he looks confused" and those that know me would illustrate it as "Oh God, he's looking for a new place to shoot again".
How do I use my hand? This is the easiest way to test light and you're all capable for doing it.
Put your fist up, and tuck your thumb into your hand. Look at the photos and it'll make sense. Everyones face is obviously different we all have a nose, brows and eyes. Those 3 guys vary greatly from person to person. This is a basic breakdown of the human face. The brows usually create large shadows when the sun is overhead, and you'll see if that happens when using your hand. The nose creates a show on either side or even below, you can see that. And you'll be able to see if light will reach the eyes or you'll have to adjust accordingly.
You'll see my hand in various positions near a single window light. This demonstration is less about the exact angles and more about showing you how to test lighting with your hand.