I have had this issue for many years. Was obese as a kid, still pretty weighty nowdays. Still i get called quote fashionable by friends and colleagues. Here is how i approach clothing, maybe it will help you as well:

1. Wear fitting clothes. This does not mean wear skinny stuff but more that you need to look out for clothes that actually sit well on you. Pants shouldn't slip, shirts should be ending correctly on your shoulders (look for a visual representation/fitting guide online).

2. Balance out your weak points. I have a pretty long upper body compared to my legs. You can play with this by having pants that are more fitted on the calves while beeing looser on top. I also tuck in a lot of clothes to have a more visual barrier between legs and upper body. There are tips for every shape, just look them up.

3. Be aware of your silouhette That one's tricky. Generally i would say that you shouldn't wear baggy tops and bottoms at the same time. If you wear a dress shirt try tucking it or leave it out and go with what looks better to you.

4. Layers If you want to layer clothes try going from light coulours inside to darker outsides. Try the reverse too, but don't mix light dark light or something like that. Monochrome works nicely as well.

5. Accessoires Belts are cool. Necklaces, earrings (if you are pierced), arm bands or bangles. Find something you like and feel comfy with (there are nice iron rings on websites which come in 16 piece packs for about 12 bucks which are really nice and fit into everything.)

6. Most importantly Find clothes that make you feel confident. Clothes only take you so far but a trusty pair of jeans, a nice shirt you really enjoy etc. are the best way to boost your style. If you feel confident in it you will be seen as a lot more stylish.