I would also recommend setting up a bank account off your main business account to accrue the vat you recieve from client payments. Then it'll all be there for your quarterly return.
It appears you already have the business so I am not sure registering for VAT will help you. In fact if you charge VAT and dont get paid by a client you will have to pay the VAT man at the next return. This will also hike your price by 17.5% and if you don't but much that you can claim back for then it's IMHO not worth registering.