Everyone just seems to think that Ireland is all about booze and religion. Just like any other country with a strong religious background there are certain ways to act but since it's part of Western Europe it is forward thinking so where does this balancing act draw it's line?
Don't get offended
The Irish like to poke fun and make jokes. Don't take offence, strike up a conversation. Unless they want to beat you up then run... On the other hand, like the British, swearing happens a lot. It's normal and adds punctuation to sentences.
Drink in rounds
A lot of times when you are in a group then you will take part in the round system instead of everyone just buying individual drinks for themselves. This really controls how fast you drink as you should wait until everyone is done or almost done before the next round arrives. If you are a fast drinker, you've been warned!
Don't fake the accent
I feel that no matter where you travel this is true. While imitation is a form of flattery you will probably just end up pissing people off as they will assume you are making fun of them. Just don't do it.
England
They are not British, they don't sound like thee English, and they want nothing to do with them. That's why they split in 1921. They are not ruled by the Queen of England and this can be a really quick way to piss an Irish person off.
Topics of conversation to skip
Leprechauns: Yeah, sure they are known for them but they are sick of hearing jokes or talking about them.
Do you like Guinness? they are raised on it, don't even bother with asking as its rhetorical.
Asking if their accent is British. If you can't tell, don't ask.
How do you speak Irish?: It's called Gallic and usually is only found in smaller towns
How overrated U2 is or asking how often they hang out with people or even if they know them.
Can you teach me to river dance? Do a jig!
Do be original.
A polite conversation starter will do and will probably lead into controversial topics of conversation that most North American's are told to not to bring up. Makes it interesting though and great way to learn how things are done across the pond.
Spit your beer out
If you take a sip of beer, swallow it and order something else. If it's Guinness make sure it goes all the way down as the best way to insult an Irishman is to tamper their sacred beer.