This tip is an oldie, but a goodie. And one you've heard a ton from your mom and grammy.
Stand up straight! Go stand in front of a mirror. Now stop cringing, you look fine. Now experiment with different postures from the side view and front view.
When you round your back, you lose an average of 3 inches in height, but gain a nice big tummy roll. Happens to the best of us. I am notorious for this. I have a very rounded back, and horrible posture from years of being heavy in front. Even know my husband regularly reminds me to straighten up.
Another thing to try is whether you prefer your look with hips tucked in or butt out. Look in the mirror and try it. If you have a J.Lo booty you want to flaunt then go for it. Notice the way it may also puff your chest and ribs out, depending on your shape. For me, when my hips are tucked underneath, I seem to have a longer, leaner look.
Experiment and see what suits your frame the best.