You can find out which festivals are going on here.
Interspersed in this article are pictures from the "rape and cosmos festival" in Guri, near Seoul. That's rape and cosmos the flowers, not rape and cosmos as in Kobe Bryant and Carl Sagan.
1. Scout, Research, Plan, Reserve
These festivals don't always happen in one place, and if you zig, instead of zag, you might miss the best parts, and come away from a festival thinking "weak sauce" instead of "wowza."
The best thing is to go with someone who's been before - even better if it's someone who knows enough Korean to get around, read the schedule or (glory of glories) research it online in Korean (there's always more info in Korean than in English).
However, most festivals these days have websites... and even websites with (some manner of) English on them. Don't count on that -- the English part might not have been updated since 2008, but it can't hurt to try. Use Internet Explorer, and turn off your popup blocker.
Before you show up, have an idea of what you want to do, or at least the most important bases to touch. If you just show up and wander around, you're going to catch the butt end of the fun.
If you don't have a car, know the transportation available. Know the phone number for the local taxi company, and/or the tourist help number for that region. If you do have a car, know where parking is, and how far it is from the venues. Whenever you can, get a bead on the nearest bike rental place, and use bikes to get around. Bike rentals are available in many towns around Korea, and they're an awesome way to get around.
Make hotel reservations. Well ahead of time, if at all possible, or you might find yourself up a creek, knocking on lodging establishment doors at 2am, sleeping in an elevator in a jimjilbang (a friend even got turned away from the local jimjilbang, because it was all full up, once), or having to stay out all night. The smaller the town where the festival is located, the less likely they'll actually have enough hotel space to accommodate the entire festival crowd during peak times.
(in Guri, people were digging holes in the flowers to get those cute "face in the middle of flowers" pictures.)
2. Have your gear ready
The best way to have a terrible time at a Korean (or any) festival, is to show up empty-handed, only to discover everyone but you knew that the toilets wouldn't have tissues, or that water wouldn't be available on the premises, or that the nearest non-cotton-candy food was a 30 minute walk away, or that there was no. shade. anywhere., or that the cash machine you passed on the way out of the train station was the last chance for a 30 minute bus-ride in every direction, and they don't take cards here. Some festival locales are nearly barren the rest of the year - the cosmos festival is just a park for most of the year, with public park amenities, not major festival amenities, so some of these festival grounds won't be equipped for a whole lot.
To be prepared: bring these items:
-Enough cash to taxi around, and not need to visit an ATM.
-An extra layer (best of all if it is wind/waterproof, especially if it's a spring/autumn festival: the temperature really drops at night).
-Enough liquids to survive a sunny afternoon.
-A package of napkins that can double as toilet paper in a pinch.
-Trail mix, health bars, or something in case there's no food other than cotton candy and stale churros on site.
-Sun protection (I always bring a hat when I'm at a festival).
-A fold-out mat to sit on the ground
At the train or bus terminal, find a tourist information center, and get the map/brochure they're handing out. The person at the tourist information center might be the last person with (somewhat) competent English you come across, if your festival is in the countryside, and if the festival brochure has the word "Traditional" somewhere on the front page.
(I love taking pictures of people taking pictures. Don't know why. Silly photographer poses have got to be one of the reasons, though.)
3. Be Ready for Crowds, And Ready to Wait
One of my more recent "least favorite things about Korea" is that, while there's lots of cool stuff to see and do in Korea, anything that you can see or do that is even remotely seasonal (festivals with a time frame, natural phenomena that have a time limit, like spring blossoms or fall colors) is subject to an absolute rush of people wanting to enjoy that same ephemera, at the same time, as you.
So... there are tons of cool things to see and do... but you'll share most of them with a million other people also wishing to see or do the same things. This is especially acute for famous festivals, festivals near urban centers, and festivals celebrating seasonal things, (flowers blossoming, leaves changing, butterflies mating). So be ready to wait in line, to get jostled, to wade through crowds, and to nearly lose your travel buddies a few times. Be mentally prepared for it, too, because if you're expecting to get away from it all, but discover the "it all" you wanted to get away from is waiting for you at the festival site, the unexpected stress of crowds is a lot tougher to manage than the expected stress of crowds.
(A double rainbow pose! What does it mean?)
4. Have the Right Travel Partner
My mother-in-law likes to travel old-school Korean style: with a checklist and four destinations before lunch. I like to throw the plans out the window and spontaneously take a nap under a nice tree, because it's there. Be sure you're traveling with someone who has the same travel style.
(The classic "proposal" photographer's pose.)
5. Know Where to Be... and Know that Everybody Else will want to be there at the same time
Here's where a little research is handy. The highlights of the festival will be at certain times and certain places - the Andong Mask Festival's fireworks are something you'll remember for your whole life... if you know when and where they are.
The thing is, those other million people who came to the festival? They also want to be there for that, so be ready to show up at or near your vital locations enough ahead of time that you don't miss them while waiting for a bus that isn't packed like sardines. As I said: some of these places don't have the transit infrastructure to conveniently transport the full number of visitors, because the festival crowd is double the busiest day they ever have during the rest of the year. So be ready to move early, or by a different route than others take (if you know the area), or to fight and claw for a taxi.
My wife always teases me because she knows all the different types of flowers, and my flower vocabulary goes like this: "The pink one. The pale blue one."
I've had great times at festivals; I've also had horrible times at festivals in Korea, because wifeoseyo (girlfriendoseyo) and I were unprepared, or had faulty expectations, or under/overestimated distances, crowds, or prices. If you're cool with flying by the seat of your pants, do it, but at least know where you're sleeping, and where and when the bus leaves, or you might spend most of your trip wandering around aimlessly, trying to find a way out of a neighborhood where there's not much to do.
and one sunset photo from a birthday party I went to on Friday.