Natural light is a great way to get really professional looking light without using a lighting set up. While lights are nice to have, they’re expensive and not always convenient. Nearly every portrait I’ve ever shot on my own (meaning, not doing something in a client’s set up) I’ve shot only using natural light.
Now, that’s not to say that natural light can’t be tricky, or that there aren’t ways to harness it. There are! Your best friend will be a reflector. You can buy these for not too much money, and they come in many varieties, including silver, gold, and a matte white. Silver will throw off bright, cooler light. Gold will throw off bright, warmer light, and the matte white will give a diffused, gentler light.
(If you don’t want to buy a reflector, you can make one. Foam board and tinfoil and tape. Do one side with the shiny side out, one side with the matte side out. This is actually taught by real professors in NYU’s film department so you know it’s legit. And cheap. Mostly cheap. It does really work, though.)
So, head outside with your reflective device. Angle the reflector so you get a nice fill on the subject; under the eyes is going to be your main point of focus. You want to make sure the brows don’t cast a shadow over their eyes, especially for acting head shots.
Another solution are light rings and light boxes. They come in varying degrees of quality and price, and there are a lot of great resources online for how to make your own. That being said, I would still pick a reflector. It’s easiest to set up, doesn’t run out of power, and throws off really beautiful light.
Along with that, you’ll want to do shallow depth of field and not position your subject right up against a drab wall. Finding a location that’s not distracting but doesn’t scream school picture day will go really far to elevating the professionalism of your portraits.
Hope that helps!