Ok the most major thing to know about tracing Irish ancestors is that in 1921 the building that had the majority of Irish births, marriage and death certs was blown up and destroyed during our civil war.
All is not lost though, as this is your first place to start The National Archives of Ireland
http://www.nationalarchives.ie/ and their list of genealogy websites
http://www.nationalarchives.ie/genealogy1/genealogy-websites/ You can request copies of births, marriage and death certs and they will post them to you
You can also search the 1901 and 1911 census and fragments of census from 1821 to 1851 here
http://www.census.nationalarchives.ie/
Another two good places are
https://www.irishgenealogy.ie/en/ and
http://www.findmypast.ie/
If you get to a stage where you know an ancestor came from a specific Catholic parish and you have an approximate year of birth baptism or marriage you can write to the current Parish Priest and request a copy of their records for that person.
