Put your thumbs right on your bottom ribs.
Put your middle fingers right on your hip bones.
Now, without bending your upper body forward, try to bring your ribs and your hips (your middle fingers and your thumbs) closer to each other. Essentially, you’ll be flattening out the curve of your lower back. You should feel your abs flex. If you can’t figure out how to make this work, try squeezing your butt. That usually forces your pelvis into this position.