Hi charby,
Basically you just keep going backwards in the parish registers. From ages at death you can get a rough idea of birth date; from the census, you get a rough idea of birth place. Then you start looking in the parish records - the IGI on the Familysearch site is always a good starting point, but only as a guide. Depending upon the geographical area, you may find some transcripts online.
Since you have already reached 1801, it seems as if you have already had some experience of searching for parish records before civil registration began - is this right? Before 1801 is really no different. You just have to use slightly different records to help you out and most of them will be held at the county record office. Some may be available at your nearest large reference library. Your local LDS Family History Centre is also another good place to look for parish records.
Marriage records 1754 onwards usually give the parish of residence (not necessarily the same as parish of birth), but they don't give fathers' names. Depending upon the family's status, settlement records can also useful, where they survive. Wills and property records are also another useful source. Some burial records are handy as well, especially if looking for an unusual name.
This may sound rather vague, but without knowing what resources you can readily access, it is difficult to be more precise. Hope this helps anyway.
Nell
