Fortunately it does get easier, especially if it's more than just a one day class. Try taking a deep breath, and then prepare to do these tips for before you arrive.
2. Have a hungry dog - not a starving one. If their too hungry they'll only focus on the treat; but if they're full, they won't want to work for the treat. So feed him/her maybe half their food in the morning and then (if you don't give them a lot of treats,) give the rest when you are back at home.
3. Bring yummy treats - dogs get bored of dog food or the same packaged treats. Spice it up a bit! If you usually take dry kibble, nearly anything will be better. I usually take mini marshmallows cut in half, but sometimes I bring lunch meat or hot dogs. (Need more treat ideas? Check out these 6 quick treats that you most likely already have on hand!)
4. Arrive early - We usually like to arrive about 15 minutes early to a training class because it helps the dogs become familiar and calmer in the area.
5. Work them - I've found that once we're there and other dogs start arriving, Noah is easily distracted. To keep him from being worried about other dogs near him or from getting too excited, I work with him. "Down. Sit. Watch. Down. Lay [laying head down]. Stand. Sit." - just basic, easy commands to help him focus his mind on training with me. "Touch" is also a good one to play with your dog, and you can do many different variations: high, low, make them touch near their tail...
These tips work not only when you are going to a group training session, but also when you are going to train at the park, a store or any other place your dog is easily distracted. You can also use all these tips on regular vet visits to make the visit more positive.
Have a blessed and happy day!