To play the blues properly while sitting down, stick to the following steps:

1. Sit in a comfortable desk chair (one without arms), stool, or straightback
chair. A couch is too relaxed for serious study (though you can certainly have
fun with your guitar as a sofa spud — after you’ve put in your serious practice time)!

2. With feet apart, sit up straight and forward in the seat of the chair so
that you place some weight on your feet. Because the exact position is largely a matter of personal comfort, you can experiment to find the best position for you.

3. Put the waist of the guitar on your right leg, pull the guitar up against your body, and place your right arm over the guitar’s top edge to hold the guitar in place. When you’re sitting, your right arm holds the guitar to keep it from falling forward or tipping to the side toward the headstock. You won’t have this problem if you wear a shoulder strap, which balances the
guitar in place. But take care when adjusting your sitting position so you don’t let the guitar fall.
Don’t support the neck with your left hand because you want this hand to be free to move up and down the neck without the burden of also holding up the guitar.