Here's how to hold your bass guitar properly while sitting. You want the bass to balance on your knee so that it's not tipping one way or the other. That's different for every instrument, so I suggest putting it on the knee that you're going to be resting it on and allowing it to balance itself. In this case I have to push it a little further towards my right hip so that it doesn't tip head forward, because you don't want to be thinking about balancing the bass while you're trying to play the instrument. Once it's just in position, you can put your hands in place. And if it's comfortable and you're not using your hands to actually balance the instrument all the time, then you're in a proper position to start playing.