I was taking my dog to classes with a personal handler (while she was running in a ring she was always trying to sniff something) and it helped us a lot. I think that it is great when you can afford it and you have sufficent time for that as well. What concerns the preparation, I washed my dog, wiped the undereye areas, cleaned ears and that's it. And in many sources it says the same, for example this post on grooming
. As for the claws, I have a chihuahua so I need to cut her claws regularly, approximately once in 3 weeks. And since I have a long coated chihuahua I cut the fur on the inner side of a paw so she wouldn't slip on the floor.