Light is what makes photography. OK, a little more then just light, but without the ability to capture, bend and manipulate light, photography wouldn't exist and if it did, it would be really boring. Since we've already covered color temperatures and setting your white balance manually, this article will focus more on the trickier subject of indoor lighting.
Shooting inside can be one of the most frustrating and difficult things to master for any photographer because the number of variables seems to a million. Each bulb that illuminates any part of the scene has a color, as does the natural light flooding in the windows, but what about light that bounces off a taupe wall and a creme colored ceiling? Even a neutral light source like the sun showering in a window could become colored due to the materials it reflects off of. These factors must all be taken into consideration when shooting inside.
Whenever possible, set a custom white balance for the area in the scene which is your main focal point. This will ensure the color is correct for the most important part of the frame. If you're shooting people, you want their skin tones to be a natural color, the rest of the room should evoke the color that your natural eye sees it, warm or cool.
Try to avoid using flashes of any kind. This may mean boosting the ISO and shooting more wide open, but the end result will be much more pleasing. If possible, use reflectors to bounce the natural light where you need it. A 5-in-1 reflector will give you a few options to warm or cool the area you are illuminating. If you must use a flash, bounce it off the ceiling or wall to help reduce the shadows.
Indoor lighting also lends itself to larger venues, say sports events on any level. If there is no where to bounce a flash and / or your subject is more further away then the guide number of your flash will allow, raising the ISO level and shooting with fast glass wide open will be your only option. Indoor high school sporting events like volleyball, basketball and wrestling are among the toughest indoor lighting conditions any could ever face, a monopod could very well be your saving grace.
If you are shooting architecture, get yourself a solid tripod to work from and a light meter. The tripod will allow you to setup the camera and frame the shot while you take meter readings from around the room. Utilizing reflectors, flags and diffusers will help you get a more consistent reading with your meter across the room, so no one spot is over or under exposed.
When shooting candid photography inside, say following a toddler around the house or a birthday party, setting up reflectors, closing curtains for windows and other techniques just aren't possible. You're best bet is to utilize an off camera flash (to help reduce red-eye) and diffuse it, with an omni-bounce, or Phong device coupled with wide open apertures and doing some exposure compensation as needed.
Lastly, be aware of your surroundings. If you use a flash, try not to position yourself in front of windows, mirrors, TV sets or framed art as the glass will reflect something nasty back to you.