Sit up straight at the edge of your chair. Be focused on the music. Your body posture tells your brain the degree to which you are interested in something. Be engaged!
The waist of the guitar will cross your right leg at an angle, but not a right angle.
Your right arm will support the guitar so that the left arm (fretting hand) is free to move about the fretboard.
Do not tilt the guitar back too much toward your body, you can lean slightly over the guitar if you need to see what your left hand is doing.
Your left hand thumb should be positioned just above the center of the back of the neck. Point it towards the headstock of the guitar. DO NOT let your thumb ride over the top of the neck of the guitar.
Do NOT let your left hand “hug” the neck. Keep at least a pens width of space between the neck and your hand.
Let your fingers arch and make contact to the strings using the fingertips.
Strive to produce a good clean tone with no buzzing or muffled sounds.
Do NOT bend your left wrist. Keep it straight or cock it back slightly.