Position changes are super important in both obedience and rally! Your dog needs to do position changes both in heel position (without going wide) and in front of you (without creeping in). Platforms can help teach your dog both of those concepts!
The position changes are sit, down, and stand. Your dog should be able to do these in any order — in other words a sit to down, down to sit, stand to down, stand to sit, sit to stand, and down to stand.
You'll need a platform large enough for your dog to stand and lay down on. It doesn't need to be as narrow as a sit platform, since some dogs like to stand with their rear legs a bit wider than the front legs. It can even be something like an agility table, as long as your dog can lay down on it.
Position Changes in Front
Before you start the platform training, you'll want to make sure your dog is able to do the position changes right in front of you. You can use a verbal only or a signal, but be sure it's a signal that you can do when you're not close to the dog (ie; not pointing at the ground). At this point, I like to have the position changes on verbal only, and I add the signal as the dog is further away from me.
You also need to ensure that your dog is comfortable getting on the platform and that he/she understands staying on the platform is rewarding.
Here are a few videos of me working with position changes with Excel. With all of these videos, I'm spending a lot of time rewarding stillness in between the positions. Excel is very quick to offer movement so I spend a lot of time reinforcing him for not moving! In the second video, you can see how I handle his mistakes.
When I first start teaching positions, I am careful to only work one change at a time. I will lure the dog to the starting position, then cue the change, reward, and start the cycle over. When your dog is more experienced, you can start mixing things up, but if you start getting a lot of mistakes and confusion, go back to practicing one at a time.
Here is an example of me only practicing one change: the stand to down. I cue the down, then reward so Excel stands. Halfway through the session, I switch to rewarding both in position and rewarding in a stand, to set him up for the next rep.
When my dog is doing really well on the position changes in front, I will slowly start to add some distance. At first I only go back one step, but as the dog gets more confident I will go back another step. I always walk in to reward my dog and am careful to watch that the dog doesn't step off the platform or for any forward movement.
Position Changes in Heel
Once your dog understands the positions in front, you can start training positions in heel. Depending on how wide your platform is, you can either stand next to the platform or on the platform. In the following videos, I'm standing with one foot on the platform. There's not enough room for both of my feet, but if I don't stand on the platform Excel could be crooked.
Here is Excel working on sit and down.
This video shows stand to down:
And here is sit to stand:
Building Your Dogs Skills (And Removing The Props)
Once I have nice position changes on the platform at a good distance, I will start to use some other props to help the dog generalize the behavior while encouraging the dog to stay out. I use a front foot platform and a barrier of some sort, like a gate.
I also mix up my rewards, sometimes sending the dog behind him/her to the toy or treat, sometimes releasing to my hand, and other times rewarding in place. Once I've gone through this process, it's relatively easy to fade the prop and maintain your dog's perfect position changes!