Step By Step process

It's a very tough market to get itno to be honest becasue of the fake clothes on the market, you will need a good website, Marketing, Suppliers, Logo and some clients.

If your looking for a supplieer check - The Wholesale Forums
Looking for a website check - Graphic Design Coventry
Looking for Business Start up advice - Business Link
Business Networking try - UK Business Forum

If you need some more help feel free to PM me

You will not face much problems in the business if you have 4-5 clients in hand at the beginning...because if they like your work then getting more clients will not be a problem further....