What saves the most amount of time when researching using the General Register Office Index is to work with a sound knowledge of the facts about your ancestors, where they should be located, therefore u need to know the Registration District that covered that area from 1837, (1854 for marriages). ( I use St Catherine's House Districts by Ray Wiggins, which is very simple to use.) You would also need to have looked at the Census first to identify any children, therefore you will be able to find their registrations of birth. Remember it is not always the case that a couple married before they had children, and even though on the census return this may look like a married couple, in civil registration they may not be legally married until the registrar has issued a legal certificate, therefore Catholic marriages, which were not legal until the early 1890s, if they took place without a registrar present, were not legal. Though not many lower classes could afford to be Catholic, the Church provided poor relief.