Try not to use a flash for indoor shooting, whenever possible. The harsh light from a direct flash will often make your pictures look (yeah, you guessed it right!) harsh. If you really have to use a flash, bounce it off the ceiling. A flash with a tilt head will serve the purpose for this technique. Bouncing the light will give a flattering effect to the picture.
A tripod is extremely necessary, while shooting indoors, when shooting at slow shutter speeds (below 1/30). You will need to use a high ISO setting (maybe 400, 800, or even higher) for handheld photography.
Try using an image stabilization (IS) or vibration reduction (VR) lens to make your indoor shots steady. These reduce the effect of camera-shake and let you shoot at slower shutter speeds than what is generally possible with handheld photography. Do not use a shutter speed slower than one over the focal length of the lens. For example, when using a 28mm lens, do not use a shutter speed below 1/30.
Pic Courtesy- http://photographylife.com/flash-for-nikon-dslrs