You need to do lots of research and find out what your competitors are charging.

I would imagine it would be around:

£20 for a Westie/Yorkie
£25 Shih Tzu/Lhasa
£30 Cockers, Poodles, Bichons
£35+ Large breeds and double coated breeds

What dog grooming training and experience do you have?

Are you planning on just offereing a bathing service, or clipping?