Baggy clothes make big people look bigger. Fitted (not tight) clothes create a better silhouette no matter your size. The cliché that vertical stripes elongate the body is likely true, But in reality you must experiment with chalk stripes and pinstripes to see for yourself if they create a nice look for you.
Bulky fabrics could make one look thicker, so try fabrics that will lighten up your look. Avoid "colour blocking" instead try similar or complementary colours to keep the vertical silhouette without interruptions.
And the most important tip that is perceived to knock off 2 to 5 pounds is to stand tall!.