When I practice while sitting the guitar tends to angle up ( Basicllly what I mean is I can see the fret board. I got that Homer Simpson belly. ) When I play standing the fret board is flat messing every thing up. So I either stand or kind of half sit on a tall Bar stool type chair, keeping the guitar in the same position all the time. I also find it easier if you learn standing up, playiing sitting down is no big deal.. Putting the guitar on the left leg is also a great Idea this was already mentioned...