For your dog's long hair you're going to need a set of straight scissors for grooming that fits your hands well and has blades long enough to cut through your dog's fur. You may also need thinning scissors if your dog's coat is thick.
Brush your dog's fur out in the direction the fur grows so that it is flat against your dog's skin. Be sure to get out any tangles while brushing. Don't forget to brush the fur on your dog's muzzle and his beard.
Using a comb or a pin brush, pull the fur on the top of your dog's head forward. Be sure to pull it out of your dog's eyes and trim it to the length you would like.
Comb down the fur on your dog's ears and hold the ear in your hand so that you can feel the tip of the ear. Cut around the tip of the ear, without cutting the skin, to the length that you would like. Trim any fur on your dog's face by brushing the fur downward and trimming to the length you would like. Focus on your dog's beard and any fur that grows upward around his eyes.
Comb or brush the neck out and use a thinning shear to smooth the coat on your dog's chest. Blend this fur in with the fur on his neck until it is the length that you would like.
Lift one leg at a time and trim any uneven fur growing on the back side of the leg. If you need to trim the front side, do so with the scissors pointed down towards the toes. Be sure to keep any of the back feathers under his legs and on the back of his legs trim and tidy.
Using your scissors, trim any excess hair growing over your dog's foot. Be careful not to cut your dog's skin, but put the scissors right up against your dog's paw and cut in a circular motion around the edge of each foot.
Brush all the fur out on both of your dog's sides. Use your scissors to trim the length you would like, cutting straight across until the length of your dog's skirt is where you would like it to be. Use your scissors to trim the sides and thin out any thick areas. You can use a comb to separate clumps of fur. Be sure you blend these in as you are brushing and cutting so there are no scissor lines left behind.
Carefully brush your dog's tail out and then lift it up and cut in a curved line to the length you would like the fur to hang from the tail. Tidy up the fur around your dog's sanitary area and the bottom of the tail to keep this area clean.
Brush your dog from head to tail again and trim off, with your scissors, any stray hairs, wiry fur, or straggly areas you didn't notice the first time around.