Side pockets can add extra bulk and will often balloon up with excess water and air.
Avoid elastic waistbands which pinch soft stomachs. Your drawstring should be tied comfortably at the hips, yet tight enough to stay put with a tug.
Darker colors and vertical stripes along the sides make for a long, leaner appearance.
Don't hide behind long shorts—the leg opening should hit a few inches above your knee.