The same things that I look for offline: colour, size, fabric, style, brand, price… It’s really not very different from shopping for clothes online. The only thing that you cannot do online is try the apparels before you buy them. However, that is also true in some offline stores in India. Plus, now a few stores like Myntra are offering trial option on some of their collections.
One thing that I always look for while shopping apparels online is discounts, especially on