I would counsel going slowly and carefully, one step at a time. Obtain the certificates at every stage rather than relying upon the index alone. They contain a lot of useful information. Cross-check and double check the information on each certificate against everything else that you know, and make sure that it tallies or that you can account for any discrepancies.
The marriage certificate will be your first key document (although I would suggest getting the death certificates at the same time - as the first rule of family history research is "always kill off your ancestors"!!). It will tell you:
- the date of marriage
- the place of marriage
- the name of each party to the marriage, their condition (whether bachelor / spinster, or widow / widower), their age (although it often just says "of full age"), their residence at the time of marriage, and their occupation
- the name and occupation of their fathers (although this may be blank; and bear in mind that the mere fact the father is named doesn't mean he was still alive)
- it will show their signature, or have their mark if they were illiterate (rare in the 20th century, less rare in the 19th)
- it will have the names and signatures of the witnesses to the marriage. These MIGHT be relatives or close family friends, but they need not be. Where they are relatives they can often be the clue needed to resolve another conundrum at a later date.
It will also tell you whether they married according to the rites of the Roman Catholic church or the Established church (i.e. Church of England), or some other marriage ceremony, and whether the marriage was by licence, certificate or banns. If it was by licence, you may be able to obtain copies of the licence papers, which may tell you something more about them.
Having got your parents' marriage certificate, you will then want to identify and obtain their birth certificates. These will tell you:
- the date and place of birth
- the name(s) (but not surname) if any (you can register a birth before naming a child, so this might be blank)
- whether a boy or a girl
- the name and surname of the father
- the name, surname and maiden surname of the mother
- the father's occupation
- the signature, description and residence of the informant
- when registered
- the signature of the registrar
- any name entered after registration (only used if the "Name, if any" column is blank)
You will see that the details given of the father should enable you to cross-reference this to the marriage certificate, in order to check that the name matches. If it does not, then something is wrong. If all is well, however, they will tally, and you are starting to build up a documentary record of your family.
You will now know the names of your grandparents and, more critically, your grandmothers' maiden names. This should enable you to search for your grandparents' marriage certificates, and be fairly confident that you have the right ones when you find them. This, in turn, should tell you your great grandfathers' names, and you then repeat the process of looking for birth certificates, and so it goes on.
At this stage, I would "kill off" your grandparents - i.e. look for their death certificates; and when you have them, see if any of them left a will. If so, obtain a copy. If you're lucky, it will tell you a lot about other family members - particularly their children (your uncles and aunts). Do not assume that they have necessarily names all of your uncles and aunts in their will; but you can, at least, be confident that anyone recognized in the will and described as their child is likely to be an uncle or an aunt.
Once you get to people living in 1911, you can start looking for them on the census. The 1911 census has by far the most information of all of them and you can view a digital reproduction of the actual return completed by the householder. It contains, amongst other things, information as to how long a married couple have been married (invaluable in trying to identify the correct marriage) and how many children have been born alive in the marriage (both total number, and numbers still living and now dead). Earlier censuses (1901, 1891, 1881, 1871, 1861, 1851, 1841) have progressively less information, but nevertheless help to identify family units and relationships.
The difficulty you're likely to encounter, though, is that your family lines are in Ireland. The Irish Public Records Office in Dublin was used as an ammunition store during the Civil War, and in 1922 it was hit by an artillery shell. The resultant explosion destroyed most of the records, and therefore the available material pre-1922 for Ireland is far more fragmentary than that which we enjoy here in England. You find yourself having to rely upon parish records almost immediately, and you will need to learn your way around the Irish records. The people in the Ireland section here should be able to help you with this, as they have all faced the same difficulties.
Best of luck with your search. I hope the records will be benign, and you will be able to learn something about your family. I never knew either of my grandfathers, and that is why I started researching my family: I wanted to know more about them. Well, now I do, and a fascinating story it is ...