Verified answer

Four main things: Wig, costume + shoes, appropriate makeup and contacts (optional).

Wig: Can be bought of Ebay or other cosplay stores (I recommend FM anime).

Costume: Questions that you have to answer for yourself:

What outfit of Ciel am I going as? Can I sew? What's my budget? Do I have access to buy costumes online?

Makeup: Clear, flawless (or as close to XD) and pale skin is a must. Eyeliner, fake lashes (optional) etc.

Contacts: If your OCD about being detailed. :P

well it depends..on what do u mean....i guess you could start by getting a semi-emo hair cut, and some old styled Elizabethan Age costumes...?