Do not overlook military records, in your home country and abroad.
Our experience is the male side of the family is often reasonably well documented, but the matriarchal side is very difficult as the women come from seemingly nowhere record-wise, and there are typically a lot of female deaths in childbirth. As hard as it is to trace a grandmother, it's far harder to trace a woman who marries at 17 and dies at 19.
We were able to trace the male side back to the late 1400's but there are huge holes with the female side starting in the 1800's. Myself and about 2500 other people in North America are descendent from the same man, who arrived in Quebec in 1666. My mother's side, on the other hand, the trail goes cold around the time she was born (around WW1). Basically all we have is a very common British last name for her mother.
Irish Ancestry is not terribly hard to trace as the Catholic Church kept good records and an Irish name is typically traced fairly easily to the town or county of birth. Once there, though, the commonality of names starts to fight back. 500 years ago every fifth person in England was named "John". Most other places have similar situations with first names.
