The first thing that you need to do, is to get your dog used to the pedi paw device. Make sure that they are comfortable with the device. This is because you don't want them to freak out when the device is actually turned on.
You can also go on and place their paws in the device without it having any batteries in it. This will make them think that there is nothing to worry about and they will get comfortable with the whole thing.
Now once the dog is comfortable with the whole thing, you need to go on and place them in a place where they are sitting on your lap and you have put their paw in the device. The dog is going to be looking to move around, so you might want to ask someone else who they like to help hold them in place, so that they know that you aren't trying to harm them.
Before you place the paw in, make sure the protective cap is on, in order to prevent any injuries that might occur. Now place the paw in place, and start clipping away. Make sure that you take your time and don't rush things, remember that your dog is more than likely going to be going through with it simply because it trusts you.
Take your time, and try and do each paw after a break. You might even have to go on and do the front and rear paws separately, if your dog gets to impatient. However, you can go on and offer the dog treats once it is done with each paw, this way the dog might start to enjoy it and will encourage you to trim its nails in the future.