The next thing that will happen here is that KPj will write a brief essay that will contain enough good advice to keep you going for the next month. KPj, take it away....
Is it bad that I just wanted to say - "stand up straight" ?
Seriously though. Well, I am actually serious but, what's been said already is right. You also have the upper spine to think about. If it's hunched over all the time, with the rib cage sitting lower than it should, then it'll pop the belly out, too.
One of my girlfriends good friends is actually in great shape. However, her posture sucks. She'll often ask me how to get rid of her 'pot belly'. I just walk up behind her and put my hands around her shoulder joints and blades, and 'pop' her chest up by pulling her shoulder joint and pushing my thumbs into her middle-ish traps.... Job done. It's been several weeks since she first asked me, and several times that she's asked me plus, several times that i've 'fixed' it but, she still thinks i'm joking.
What i'm getting at is the 23/1 rule. You have 1 hour in the gym to make things right and another 23 to screw it all up again - walk tall. It'll 'feel' stupid but it'll actually 'look' better.
I have this subconscious 'cue' in my head that makes me think about my posture everytime I walk through a door. I seen somewhere, sometime that when you walk through a door, your chest should go through first. I thought about it a lot and now it's habbit....