Good links.
Assuming that you have found ancestors on the US censuses, collect up the names and ages of any born in Ireland, then try ship records (Ellis Island is a good starting point) to see if passenger lists give any helpful information.
Irish records are tricky as many were lost and not all the surviving records are online, so collate what you can, then post queries on this site and you will find many helpful people with a wealth of expertise.
Good hunting!
Philip