Lighting is one of the most vital elements in photography and can dynamically change an image. Here are some easy ways to improve your techniques and take better advantage of your light.
1. Stop using your camera's built-in flash
The on-board flash can help out in a pinch when no other lighting is available; however investing in a speedlite, or light panel can drastically improve your photos. While some models of camera do allow the pop-up flash to be adjusted, it's often a tedious process of navigating menus, and even still they have a tendency of being overpowered. A secondary issue with on-board flashes is they lack any form of diffusion, coupled with the fact that they're aimed directly toward the subject, the resulting photos often have a blown out look, with an underexposed background, and unnatural shadows (think Polaroid instant photos). Lighting tends to look best from an offset angle, rather than head-on, which leads us into our next tip.
2. Create directional lighting
This is where off camera lighting really comes into play. By having your light source slightly above eye level, and around 45° to the side, you can create natural looking shadows and more distinct separation between your subject and the background. A light panel is great for this, as you can see how the light falls as you move it around, but this technique can also be achieved by using a flash with a PocketWizard, or other remote trigger. Try to avoid light from beneath your subject's eye level, or from directly behind the subject, unless you have a reflector, or some other light source to fill their face.
3. Take advantage of natural lighting
Available lighting is the often the best lighting, as it's all the light you've got to work with; so it's vital to know how to make it usable. Unless you have some form of fill light, it's best to place any light source behind you (the photographer), so that your subject is facing towards the light, even if not directly. Available lighting is also crucial for night photography, with streetlights and neon's providing unique opportunities for amazing photos.
4. Wait for sunrise or sunset
Midday, with light from vertically above a subject, tends to create very unappealing shadows, and harsh lines. Oftentimes it can be more advantageous to plan ahead and shoot earlier, or later in the day, when the sunlight is more directional. This also gives you much more leeway to play with how the light falls on your subject by rotating them, and yourself, and experimenting with the different shadows, and highlights created.
5. Look for diffused light
If you have to shoot during midday, or in otherwise harsh lighting conditions, hard shadows can be made softer by finding an area where the subject can be in less direct light. This can be achieved by holding a diffuser above your subject (that semi-transparent white thing that might have come with your reflector), by finding some nice shade, waiting for a cloud to occlude the sun, or (when applicable) moving farther from your light source to take advantage of the inverse square law.