Those are some really great tips from meeko_33785, and very helpful with the show times! I think I read a post in another thread that the last showtime of day is the least crowded, but it's a large theater and there are usually enough seats for everyone (although I've never been to WDW during Peak seasons). And there are no bad seats. The show is performed "in the round" so the seats are on all sides. You may think that a certain seating section might be better than another, but the show does a great job of giving you a great view no matter where you sit.
During my last trip, I saw FoTLK twice and both times showed up about 15 minutes prior to showtime with plenty of seating still available. However, if you do have kids that want to get involved in the "interactive" portions, you should probably get in line a bit earlier (at least 30 minutes prior, and possibly earlier) to increase your chances of sitting in the front rows.
It's a great show...my favorite in WDW. I hope you enjoy your trip!!!