the judges are sitting down a few feet from you so you want to make sure you are posing to them and not the audience...the front lat spread........ like oldfella said most will put thier hand way too far in fromt of thier abs, you want to put them on the sides adn push in on your obliques, this will make the waist smaller and the delts and arms will show more defination from action of pushing on your sides...fill your chest with a good breath of air and try to keep your elbows hands and shoulders all aligned on the same plane (think of lying face down on a piece of glass and hitting this pose, everything should be on the same plane) hope this helps....
the rear lat spread is diffacult as well, i would do kinda the same thing as the front but get a camera and have someone take pics with you moving around a bit untill you find what looks best... everyones physiques is different so thier is no cookie cutter instructions for the poses....