You'll require the following three pieces of information if you wish to start a successful search for Irish ancestors.
1. Denomination. 2. Parish. 3. Townland.
You'll have to rely on Church records as your ancestors were born before Civil Registration was introduced in Ireland. Non Catholic marriages were registered from 1845 onwards. When registration for BDMS started in 1864 some people didn't bother with the registration for a few years after that date. Keep your fingers crossed that church records still exist.