what should I wear while writing?

If you are a woman, perhaps nothing.  The Guardian reports that:

Our survey of women writers revealed that only 48% wore "normal" clothes to write in. Two per cent wrote in the nude, 14% wore night clothes and 1% have a "special writing outfit".

The writer, Hadley Freeman, suggests that in addition to the proper selection of writing attire:

... I would suggest this for, to borrow your deliciously romantic phrase, "the aspiring authoress": first, a giant padlock. This is to be draped decorously around the fridge. It's amazing how hungry one gets when one is working from home, and how fascinating heretofore uninteresting foodstuffs become. Eating a can of pickled onions or starting the next chapter? No contest!

Next, a pair of shoes with cement blocks for soles. If you can't find them on the high street, ask a friend with connections to the mafia. Put them on once you have finally watched all the morning TV you can take before suffering an aneurysm and are sitting at your desk. These will make it harder for you to get up and wander around: it is an unexplained but irrefutable phenomenon that for some reason it is only when one has to do any kind of writing at home that one realises how many fascinatingother things there are in one's flat that require reading immediately, such as three-month-old magazines and the backs of aspirin bottles.

Next, maim your left hand. Just smash it with your cement shoes and be sure to injure it in a way that won't impede your typing, but will stop you turning on your wireless or spending another day on the internet reading articles about things you don't care about.

And finally, don't wash your hair for several days and wear the ugliest outfit possible. Perhaps that old maternity dress of your sister's that somehow ended up in your closet? The one with the spaghetti sauce dripping down the front in a pattern that makes it look like you're drooling? Perfect. Put that on. Thus, even if you develop the thigh muscles to be able to walk in your cement shoes (never underestimate the determination of those desperate to procrastinate), this look will definitely keep you from going outside and will secure you in your chair, writing the next great novel. Procrastination is a strong compulsion, yes. But vanity beats all.