Only use camera gain as a last resort, when there is not enough light and you cannot illuminate you subject. Remember that it will add noise to the signal which can create problems in post and at transmission.
Always use a tripod when you can. Steady shots should be the norm.
If you do need to work handheld, you will get much steadier shots if you use a wide lens and get close.
White balance adjusts the red, green and blue outputs of the camera to be equal. It is used to remove colour casts created by imbalances in the light. Always remember to white balance as the light changes throughout the day.
A zoom lens can affect focus and exposure as well as the size of the picture.