Where do you love, what bike do you ride, and what are your goals?
Jimmy Lewis has a good school that sometimes is big bike oriented, I've done one and loved it. Many skills from little bikes are similar but many are different.
I ride a big bike mostly these days (KTM 950, sold my 450 I just wasn't riding it much), and would be glad to keep you posted on rides but I'm in Atlanta. We ride in north ga but sometimes highland park. That's a good place to practice as the trails are marked with difficulty so you usually don't get in over your head. The biggest thing is tires. If you plan to ride off road, you need to have GOOD tires on the bike unless it's very dry. Oh yeah and be willing to toss your bike down the trail. Lol.