This is the essential oil blend suggested as a tick repellent:
equal parts of:
Cedarwood
Lavender
Citronella
Thyme

You can also add lemongrass and/or peppermint.

Put the mixture on a brush and run it through the fur, or put several drops of the mixture at the places ticks most like to attach -- behind the ears, under the armpits, on the head and neck.

You can also make a repellent collar by soaking a soft material collar in this mixture (1 drop of each oil), plus 1/2 teaspoon alcohol, plus 4 garlic capsules (or 2 drops of a mixture of 1 teaspoon vegetable oil plus 1 drop garlic essential oil).  This collar will last for about a month, then you can re-apply the oils.  This is more effective as a flea repellent, though.

To detach a tick, place 1 drop of Thyme oil on the tick.  After it detaches, use several drops of Lavender oil to disinfect the bite wound and prevent infection. Repeat frequently.

Essential oil flea treatment:

Take a steel brush and a piece of absorbent material (like terrycloth) the same size as the face of the brush.  Pull the material down over the teeth of the brush, so that it lies about 1 inch above the base, depending on the dog's/cat’s length of hair.
Prepare a bowl of warm water and mix in 4 drops of cedarwood or pine oil, and soak the prepared brush in this before brushing the dog's/cat’s coat.  This treatment will disinfect the dog/cat, condition the coat, and collect the parasites and eggs in the brush.  Rinse the brush thoroughly several times in the essential oil water several times during the brushing.

You can also make a flea collar by soaking a soft cloth collar in the following mixture:
      Alcohol 1/2 teaspoon
      Cedarwood 1 drop
      Lavender 1 drop
      Citronella 1 drop
      Thyme 1 drop
      4 garlic capsules, or 2 drops of a mixture of 1 teaspoon vegetable oil and 1 drop garlic essential oil

Blend together, pour over the collar.  Allow the collar to dry before putting it on your pet.

Also add a capsule of garlic to your dog's/cat’s food, to help repel fleas.

Use borax or the commercial preparation called "Flea Busters" (also contains borax) in the carpeting, furniture, bedding, etc. to kill the flea eggs and larvae.  Vacuum up excess borax.