Before 1837 you are dependent on parish registers ("PRs") as your principal source. A standard, pre-printed format was introduced in 1813. Prior to that, what was recorded was often pretty much at the whim of the minister. Essentially, the further back in time you go, the less information you get.
A good way to get the hang of searching PRs is to start with the births, marriages and deaths you already know about from the 1840s and 50s and see if you can trace the corresponding baptisms, marriages and burials in the PRs. A couple of words of caution: in the early days of internet genealogy, the databases didn't tend to give you the PRs from after 1837, because the assumption was you would use the BMD records ... this is being addressed now, but I do not think the work is complete yet. Secondly, just because somebody was born, doesn't mean they were baptised either as an infant, or at all. So don't be dismayed if you cannot find a baptism to match a birth.
There are some things that come to your aid when you start working with the PRs. One is that you are into the age before mass transportation (the London & Birmingham Railway, Britain's first long-distance railway route, was opened in 1838). For the most part, people did not tend to travel long distances. And the rigorous enforcement of the Poor Laws meant that poorer people did not tend to leave their home parishes except on marriage, and when they did they seldom moved more than one parish.
The exception to this is the migration to the cities. There was a significant migration to the cities in the early 19th century. If you have labouring class ancestors in Birmingham they are likely to have been part of this. So movement through several parishes into the city is quite possible. But even so, people did not choose to go to Birmingham as such ... they went to the nearest city. So if you have a potential candidate for the baptism of somebody who ended up working in Birmingham in, say, Ryton-on-Dunsmore, then be hesitant to assume that this is necessarily your ancestor because to get to Birmingham he would have had to pass through Coventry. If he was looking for work, why did he not find a job in Coventry instead of pushing on to Birmingham? (That's not to say that he didn't - perhaps there were no suitable jobs in Coventry - but we are playing the odds here, and the odds favour that person going to Coventry rather than Birmingham).
An understanding of the geography of the places you are dealing with is going to be important in the next stage of your research. So for a while you may find that you have to stop looking for ancestors, and start looking for places instead. This is no bad thing. I have seen plenty of risible genealogy posted online by people who clearly never bothered to learn about the geography of the places where they claimed their ancestors lived, and hence had cobbled together totally implausible life stories which relied upon evidence of totally different people who just happened to share the same name. A little bit of map work can save you from this sort of error.
The Cassini Historical Map series are reprints of the first three series of Ordnance Survey maps, re-scaled and re-projected to match the modern OS 1:50 000 sheet numbers. The dates that each sheet conforms to will differ according to the map, because OS mapping in those days was a rolling process. For example, OS Sheet 177 is East London. In the Cassini Historical Map series, there is:
Old Series sheet 177 (1805 - 1822)
Revised Series sheet 177 (1897 - 1902) and
Popular Edition sheet 177 (1920 - 1922)
The Old Series is likely to be the map most useful to you if you are looking at pre-1837. This will show you the "lie of the land" at the end of the period you are researching, and enable you to see which places are where, and how they are connected by roads and canals. This will enable you to test the plausibility of the assumption that the man who was baptised in parish X was also the man of the same name who was married in parish Y and who had children baptised in parish Z.
Finally, once you are researching pre-BMD, the importance of WILLS comes to the fore. Even people of quite limited means made wills, and they give you the names of acknowledged children (and often as well grandchildren, and some siblings who might be appointed executors and so forth). This often enables you to verify the family grouping that your ancestor belongs to. So when you are looking at baptisms, don't just say "Ah yes ... my ancestor was John Jordan, and here is a John Jordan son of Philip and Mary being baptised in 1812 ... that looks like him". Make a note of all of the other children of Philip and Mary Jordan baptised in the same parish for 20 years either side of John. Then go and look for a will associated with John Jordan's death. If he appoints "my brother Zachary Jordan" to be his executor, and Philip and Mary did not baptise a son named Zachary, then you're probably looking at the wrong John Jordan baptism. BUT ... you DO now have a more distinctive name to search for. So go and search for some Zachary Jordan baptisms that fit ... and when you find one, check to see if the same parents had a son baptised called John (then check the burials to make sure that he didn't die at the age of 4 months ... ).
Hope this helps, and best luck with your researches!
