Sharing what I've learned about dressing for my body type since I started paying attention to this. I have a rectangle body shape — not much shoulder-to-waist differentiation — and learning to dress to create that shape has changed how I look in photos significantly.
For rectangles (most common male body type): the goal is to create the illusion of more shoulder width and less waist. Structured shoulders in jackets and blazers are your friend — unstructured or drop-shoulder silhouettes make you look shapeless. Horizontal stripes on the upper body create visual width. Avoid boxy fits that hang off the shoulder without tapering.
For broader/inverted triangle builds: you have the advantageous ratio already. The goal is not losing it with bad fits. Slim fit trousers that taper slightly towards the ankle maintain the shoulder-to-hip visual contrast. Avoid extremely tight things on top if you're very broad — it can look disproportionate.
For stockier builds: vertical elements (vertical stripes, longer jackets, V-necks) create elongation. Mid-rise trousers that don't cut across the hip awkwardly. Monochromatic outfits (same colour family top to bottom) also visually elongate.
Universal advice that applies to any body type: the single best thing you can do is get clothes that actually fit. Most men buy clothes too big. Shoulders should sit on your shoulder, not hanging off. Shirt torso should taper with your body, not balloon out. Trouser break should be minimal. A tailor can fix 80% of fit issues for less than the cost of a new item.
The structured shoulders in outerwear point is something I didn't appreciate until I started paying attention to it. A well-cut blazer or jacket literally builds the silhouette you want on top. Even on days when you're wearing a plain tee underneath, a good jacket transforms the proportions of your upper body.
Fit before everything. I cannot stress this enough. I see guys with expensive clothes that look bad because the fit is wrong, and guys with cheap basics that look great because they fit properly. Prioritise fit in every purchase. Particularly the shoulder seam — if that's in the wrong place you can't fix it without major alteration.
V-necks for creating an elongating visual line is a good tip. The exposed neck and the V shape both draw the eye down and make the torso look longer. Also helps frame the jaw and neck area better than a crew neck for most builds.