Many of the same principles apply to the guys:
Triangle (or pear): Use tailored blazers or jackets with structured shoulders to create shape and square up the shoulders for an illusion of balance. Using patterns on the top half and vertical stripes draws the eye upwards while colour panels across the upper torso and shoulders, balanced by darker colours around the mid-section will broaden a narrow torso while creating shape through the middle.
Oval (or apple): While more classic and simple looks in solid colours are great for slimming and framing, fit is the name of the game. A good fit will avoid pinching and wrinkles while avoiding billowing and excess fabric that ads bulk. Single-breasted, lighted tapered jackets frame the upper body, providing structure.
Inverted triangle (or strawberry): Look for slim fit (but not skin tight) shirts with a v-neck to draw the eye down. Choose straight leg – slim fit pants and jeans (but avoid skinny jeans) and look for camo or other patterns to balance your broader torso. Finish up with slim fit jackets that follow the your silhouette without being boxy.
Rectangle (or rhubarb): Use structured looks, layers and accessories (eg scarves) to create the illusion of bulk at the shoulders and styling that nips in mid-body. Horizontal stripes across the upper body (colour block t-shirts are great for this) and pops of colour or well-placed detail draw the eye and create balance and shape.