To hold the guitar properly alywas use a strap. The guitar strap will put the guitar in the same position everytime whether your standing or sitting with the guitar.

Here are a few photos of B.B. King holding his guitar that he named Lucille.

The guitar is in the perfect position and his hands are free to play versus having to hold the weight of the guitar or to balance the guitar.

Whether B.B. King lean forward or backwards his guitar is still in the same position.

Even when B.B. King stands his guitar is still in the same position.