Bring your grooming tools out and sit down with your dog for a grooming tool conditioning session before grooming. This will get your dog used to the tools you use for grooming without using actually them for the grooming tasks.
Sit on the floor on a comfortable blanket or soft bedding with your dog and your grooming tools behind you.
Introduce grooming tools to your dog one at a time. Bring out a set of clippers or a pair of scissors and set them in front of your dog and give him a treat. Without touching them, let your dog sniff them. When he does so, give him a treat.
Repeat this for every tool you have behind your back until all of the grooming tools you use on your dog from brushes and combs to clippers and scissors and even toothbrushes or cotton balls you may use for cleaning ears, are sitting in between you and your dog. Continue to not touch them. Just let them sit so your dog can explore and sniff. Be sure to treat him as he sniffs.
One by one, hold each tool up to your dog's nose and let him sniff it while it's in your hand. You will condition him to understand you will be holding these tools and he will still be safe. Each time he lets you hold a tool in your hand and sniffs it without showing anxiety, give him a treat.
Without the goal of grooming your dog in mind, plan to use each one of these tools in some way with your dog so he can hear them, feel them on his skin or in his fur, and see how they will be used on him.
One at a time, pick your tool and do one thing with it with your dog. For instance, turn the clippers on and just hold them up against your dog's skin so he can feel the vibration. You don't need to clip any fur at this point. Use the toothbrush and just set it gently inside his mouth. Don't brush his teeth, just show him where it will go.
When it's time to actually groom your dog, only bring out the tools you plan to use for that session. You may just need to brush or you may need clippers or scissors and a brush, or you may only need a toothbrush, for instance. Let your dog sniff the tool and give him a treat. Slowly use the tool for a grooming procedure for a moment and then give your dog a treat.
Continue to use this particular grooming tool to groom your dog while constantly treating your dog. A good way to avoid having to give your dog a bunch of tiny little treats is to hold a larger treat in your fist with just enough hanging out for your dog to chew on. For instance, you could wrap up some deli meats in your fist and leave just enough hanging out for your dog to stick his nose in and chew while you are brushing his body.
Practice some kind of short grooming tasks every day with your dog, using the treat and groom method to condition him to go into a grooming session calm and relaxed and knowing what to expect. Keep those rewards coming as your dog is learning as well as once he's a bit calmer before each session.