Different types of players will have different stance. Your stance may not exactly be the same as mine but there are a few guidelines to keep in mind.
Balance is important simply because a good stroke requires minimal body movement except for your arm to swing the cue stick. You need to find the proper balance so that every other part of your body is kept still. Spread your feet apart to distribute your weight evenly on both feet. Move your left foot forward if you are right handed or your right foot if you are left handed.
Your arm should be perpendicular to the table, ie. 90 degree angle (see illustration below). It should remain at 90 degrees as you swing your cue stick. There should be no sideways movement of your arm. This ensures a straight stroke.
Next, make room for your arm to swing freely. In order to do this you must angle your body at least 30 degrees from your cue stick. Make sure that your arm doesn't hit your hip when you swing back. Let yourself be comfortable with the position.
And last, you must set your cue stick as level as possible by lowering your upper body to a point where your cue stick becomes as level as possible. Depending on how tall you are, you may have to lower your body even more to accomplish this.
Head Alignment
As a general rule of thumb, your head must be aligned with the aim line. Your cue must be aligned with the center of your head or right below your dominant eye. You will have to find out which works for you. The important thing is to keep your head perfectly perpendicular to the floor and not tilted left or right. One way to check this is to video tape yourself as you are setting up your stance and alignment. Refer to the illustration below for an example of the correct head alignment.
