People
The bigger the light source, the softer the light. That's one of the basic rules of photographic lighting. Softboxes, reflectors and umbrellas act to diffuse a point source of light. When shooting with strobe or continuous light bounce the light into an umbrella or off a reflector for a softer, more flattering portrait light. White foam board makes a great reflector and is available in a multitude of sizes. Soft light works very well with portrait subjects. Portrait lighting is usually done from above or at eye-level with the subject. Light from below gives an unflattering ghoulish effect.
Food
According to writers at Foodportfolio.com, "Probably the biggest decision a food photographer will make during the creation of a photograph, is where he will place the main light." Use smaller lights to create more texture on the subject. Also keep the lights lower (in relation to the subject, not intensity) to give moist foods more texture. Avoid front lighting unless the subject demands it. Front lighting is flat and reveals very little detail and texture. Remember, lighting is all about mood. Decide the mood first and then determine the lighting that best achieves that mood. Photographer Miha Matei suggests using natural light. She says, "Use natural light whenever possible. Placing the food near a window and exposing for the food/foreground makes the background brighter and gives it dimension and depth. You will have to use the manual settings on your camera (so read your camera how-to instructions), but it's well worth it."
Jewelry
Photographing jewelry and other small reflective surfaces requires certain lighting techniques. According to Tabletopstudio.com, "Rather than flash, we like to use continuous lighting for product photography. Using continuous lights makes it easier to visualize what the final image will be like." Photographers have different preferences when it comes to the kind of studio lights used for photographing jewelry. Continuous florescent lights are compact and don't emit a lot of heat. Whether strobe or continuous light, the light is typically diffused to some degree when shooting jewelry and other reflective objects.
Wrap up
Knowledge of basic studio lighting is essential for the studio photographer to achieve her vision. Evaluate each subject for the light that best achieves this vision and make a habit of studying and learning to see light and its properties.