We talk about our posture all the time in class. Remember, having good posture is not about endurance. If you feel pain or discomfort, stop and rest. But be aware of the feeling and reflect on why it was that way. The key is the same as it was to take this awesome picture I found.
Patience and awareness. And adjust yourself until it is just right. In the picture, you knew once you saw it. With your body, you will know once you feel it.