• Sitting position with the guitar resting on your left leg (classical position) or
• Sitting position with the guitar resting on your right leg.

Gitarrero Beginner prefers the one where the guitar is resting on your left leg (see Introduction) because from experience, it seems to be the most effective playing position when successfully learning how to play the guitar.

With this position, the guitar is high enough and, due to its diagonal position, close enough to your body. Also, there is no need to twist and turn in order to achieve correct finger positions. The positioning of the left leg in an angle gives the guitar a place to rest firmly and prevents the instrument from sliding up or down.
A variation to the "classical" playing position can be to sit lower and leave out the footstool. This way, the upper leg is automatically bent while the pelvis is somewhat straighter. The guitar is also held in a similar position to that when playing standing. So, if you can see yourself play standing in the long run (a must for rock musicians!), you will avoid difficulties later if you practise in the classical position now.
Alternatively, you may choose a position, where the guitar is resting on your right leg. If you do, you should pay attention to the following:

• Do not raise your right shoulder.
• The neck of the guitar should point to the left - that is not to the front.
• Your upper body should be straighten - not bent over the body of the guitar.

As a matter of principle, playing an instrument should never require tension in any of your body parts. A general rule is: use as much force as necessary, but not as much as possible.
You should avoid the following mistakes with regard to your playing position. From experience, they can easily create problems.

• Tense shoulders which usually result from unintentionally raised shoulders.
• A bent upper body.
• Legs, that are not firmly resting on the ground or footstool.
• Tensions in your right arm's muscles.
• Tensions in your upper left arm's muscles.
• Pressing your thumb onto the back of the guitar neck.

Here is a test that can tell you whether or not you are applying the correct finger pressure.

1. Put a small strip of paper (newspaper or other) between the strings and the fretboard in the second fret.
2. Finger the E Major chord and check its sound.
3. Take out the paper.
4. If the paper comes out easily and does not tear, your finger pressure is fine; otherwise it is too high
   
   
   

Perhaps you have seen guitar players on TV or on stage that don't comply at all with the playing position described and recommended above. No doubt, there are several techniques to create the same sound and when the sound is good, the technique that was used to create it does not necessarily matter.
However, the experience of many teachers and players shows that certain techniques will guarantee good sound more often and more easily than others. Not every guitar player that sounds good uses the right technique, but all players using the right technique, sound good.