General fashion designs and accessories are made for a perfect body. It is the trend with most of the fashion designers. They cannot be blamed either since most of the people in the world are having a normal size and shape. That does not mean that slimmer men are not supposed to have fashion garments and accessories. There are some fashion trends that perfectly fit a slimmer body.
Blazer can be used as a good tool to make a slimmer person more attractive. A padded blazer on the shoulders can prove to be really worth for a slim man. However the padding should not be oversized since that can make the look even slimmer. A big padding can make the blazer look cheaper in quality as well as it will make the person look even slimmer. It should also go with the pants design. Otherwise it will look really odd in the fitting.
Pants can prove a good way to look less slim for a man. Classic pant with a flat front and a straight cut or a boot cut can be a good choice for a not too fat man. Adding more pockets to increase the volume of it is another technique used by the fashion designers. 
Selection of the fabric and the patterns to go with it will be very important in the process of fashion design. Chunky knitted wool garments can add extra weight to a slim body. It makes the person look much fat than actually he is. Pinstripes have to be avoided on these dresses. Purely because it will make you look even slimmer.
When it comes to shirts, higher thread count materials ca be useful for slim men. Spread collar shirts are more suited for slim men since it will add some more height to the look as well.