Trying to pick a day when there are good waves, is a bit of a hit and miss affair. Thankfully there are some good websites to check and see what the local weather is like at the nearest surfing spot, which for me happens to be tramore, waterford.
Some site are:
http://www.windguru.com
http://www.magicseaweed.com
But I think for the best advice, it’s better to make friends with the local surf shop guru, ring ahead and ask the whats the story with surfing that day!