It depends on your body type but there are things that help such as stylish belts around the waist, shirts with vertical stripes, wearing bustiers, or certain undergarments under your clothes. Also find clothes that are formfitting with a strong fabric therefore it can help slim the body up such as a sheath dress made of a knit fabric.
Dark colors, especially black. Clothes that actually fit you and flaunt your curves all while covering the areas you want to slim down. Stay away from stripes and bright colors. Long sweaters tend to make you look taller and leaner as well.
Wear jeans that are higher waisted. It looks horrible when a big girl has a muffin top over low cut jeans. Wear shirts the flow over your stomach and upper arms. Wear jackets that give your body shape. Keep your hair long.
Heavy but well tailored clothing could work, for example jackets and coats. Then underneath you can wear something tighter fitting but just open the top part up. Then for bottoms if you are worried about your legs you can wear a long skirt or jeans depending on how much weight is carried in your legs. This is kind of guessing (so I am sorry if this doesn't work). I am not too knowledgable about this.
don't wear boot cut jeans, they make your legs appear more stumpy and bigger. wear darker colors