Try On Brands You Don't Know
Sites like Yoox, Gilt, and JackThreads regularly offer clothing from different designers and brands at great prices. Still, you should know how certain brands fit you prior to pulling the trigger. You can ask around on the Internet and look up stuff all you want, but nothing's going to beat heading to a store and trying the clothes on yourself. Since these sites usually get stuff from the previous season, you'll have to try on the newer stuff to get a feel for how a certain brand fits, but thankfully most companies are pretty consistent with how they cut their clothes.