Read the guidelines and questionnaire two or three times. That way you will be more natural when you shop and won't panic that you forgot something. The more shops you do, the more comfortable you will get.
I agree with MF Johnston that you are not the "ideal" shopper if they do not assign the shop in a day. Once you have rearranged your schedule, cancel your application to the shop. This is better than cancelling the shop after it is assigned.