2. Natural light
When you're starting out, there's no need to go out and buy a host of expensive lighting gear when you already have a source of free light that offers endless variety. Direct from the sun, light can be a bit harsh, but when diffused through clouds, or bounced off different surfaces it can take on all kinds of wonderful qualities. Then there's the fact that it moves position and colour throughout the day, from warm and low in the morning to cool and overhead at midday, then back again. The great advantage you have with portraiture is a movable subject, so you can place them where the light looks best.
Natural light: Reflectors
Light, inexpensive and hugely versatile, a simple reflector is one of the most important items in the portrait photographer's kit bag. It acts almost like a secondary light source by letting you bounce light into shadows on the face. Here you can see the difference it makes: with the sunlight coming from behind, the reflector helps to bounce light back towards the face, evening out the contrast and adding catchlights in the eyes for a punchier, more saturated portrait (right).
Natural light: Window light
Window light offers soft, directional illumination that can fall beautifully over a face. North-facing windows are best (north of the equator) as they don't see direct sunlight. Try having the subject side-on (perhaps with a reflector to bounce light into the shadow side), or shoot with their back to the window and expose for the shadows for a high-key feel.
Natural light: Seek contrast
In most good portraits, the subject stands out from the background. One way to do this when shooting outdoors is to look for contrasting lighting between the subject and backdrop, either by having the subject in shade with a bright patch behind like this, or finding a spot where the light falling on them is brighter than the backdrop, like a doorway.
Natural light: Avoid sunlight
When the sun is out, you may think it's the ideal time to go out and shoot portraits. But sunlight can be unkind on faces. This is because light that comes from a small source is harsh, like a bare bulb; and while the sun is huge, for us it's a small spot in a big sky. So avoid direct sunlight. It casts shadows of the nose across the face, shows up spots and makes subjects squint.
Natural light: Look for shade
A cloudy sky or spot of shade is much better for portraiture than direct sunlight. In the shade, the light is far softer. It's also less strong, which might mean increasing ISO, but that's a worthwhile compromise for flattering light. If there's no cloud, look for a spot in the shade of a tree or wall. Alternatively, shade the subject with your reflector.