Being more serious, just the reverse of everything I said above (I'm sure that was obvious).
And as stated here: you have to pay attention to it. When you're training, you're so focused on just doing the surgery right that the last thing that crosses your mind is your posture, and even less commonly what effects it will have in 20 years. As you get more comfortable with the surgery part, you can start to be more cognizant of you posture. But the best thing you can do now is to make sure that you're comfortable before you even start. Unless the patient is crashing, you have a couple of minutes to adjust the table, the mayo, the video screen, your headlight, your scrub, your bovie pedal - all of those little things add up. Get comfortable. Set things up so that your natural inclination before you start operating is to be in a position with good posture.