Best time to travel to Ireland with cheapest flight ticket

I'm planning to visit Ireland this summer. My break starts in Mid-May to last week of August. I wanna know when is the cheapest to travel there in terms of plane tickets. I don't have a tight schedule or anything so I can basically take any flight any time. When and where should I get the ticket? Is Tuesday really the cheapest to fly? I'll be coming from SF, so SF airport would be the closest. Thanks!!!

Update : Also.. I have relatives in Ireland so accommodation isn't a problem. Can anyone show me a sample flight schedule with price?

Thanks again!!!

Update 2: If there's a connecting of flight stop. I'd like to have it in Spain for one of them because my relatives also have a place there so it would be nice to make use of the stop. Maybe just a couple days though on either way (on the way to Ireland or back to San Francisco).

Also, which places are nice to visit? My relatives are in Dublin and Kildare.
I know I want to visit the castles and cultural spots. Mountains are okay but I'm not much of a hiker but I do enjoy site seeing.

Thanks!

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There aren't any nonstop flights between SFO area airports (including OAK, SJC, and SMF) and Spain--so you couldn't get a stopover due to connecting there--but Aer Lingus does fly nonstops between SFO and DUB. 

Earlier is better, as most airlines begin peak season pricing for transatlantic trips on June 1. 

Using ITAsoftware.com, I see SFO-DUB with a connection at Heathrow each way for $769 currently. This departs May 13 with 1 month stay. The nonstop Aer Lingus flight is about $140 more currently. 

I would not expect fares any cheaper than this by waiting too long. In fact, for a May departure, transatlantic, I would want to book no later than 2 months advance. I would also want to sign up for sale fare alerts here:http://www.farecompare.com/search/year-h... 

If you're not staying a month (I just guessed) then you might find something better searching dates athttp://www.aerlingus.com and http://www.bookingbuddy.com 

I also checked "open-jaw" for you--arriving to Ireland, and returning from Spain--but cheapest ITA shows is $1018. To include Spain in this trip, it will probably be cheapest to book a separate ticket with Ryanair or Aer Lingus from Dublin to Spain. Those are sometimes as cheap as €20. http://www.ryanair.com

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Fly out as early as possible, prices for airfare start to rise mid-June and don't come down until October. 

SF = SanFran? From the west coast of the USA the cheapest tickets start at 900 USD roundtrip to Europe. Las Vegas especially has very good deals, look out for them. 

Another cheap option to get to Europe is http://www.airtech.com/. Just make sure that you have a way to get back at the time you need to before you use their voucher. Summer is ultra-high season and flying stand-by can be madness if you do not have the funds to tide you over another week. (Which would be 500 USD.) 

It does not really matter which one of the big hubs (Rome, Paris, London, Frankfurt) you fly into, there are cheap budget flights to Ireland from almost every airport in Europe. See http://www.skyscanner.net