First, you need the proper equipment.
1) Toothbrush- There are toothbrushes especially designed for use in pets. They have special sizes and shapes, and one model even has an ergonomically shaped handle. A human toothbrush would work fine too.
2) Toothpaste- MUST be a pet product! Human products are meant to be spit out and may cause GI upset in pets. Pet toothpastes come in a variety of flavors. Poultry is a favorite here, but there is also malt, beef, and even mint.
3) Your pet
4) Patience, patience, patience. This is a learning process, and getting frustrated will not help.
As with any other routine, it's best to begin a dental care program when pets are young puppies or kittens.
Tooth brushing doesn't happen overnight. It requires training, just like "sit," "stay" and "come." First, select a convenient time when you and your pet are both relaxed. For the first few days, simply hold your pet as you normally do when petting him/her. Gently stroke the outside of your pet's cheeks with your finger for a minute or two. Then, after a few days, place a small amount of toothpaste on your finger and let your pet sample the flavor. Many pets like the flavored toothpastes, and soon will consider it a treat.
Next, introduce your pet to a toothbrush or finger brush. Place a small amount of toothpaste on the brush and gently brush one tooth with a slow circular motion. Gradually increase the number of teeth brushed until you've built up to 30 seconds of brushing per side. It is important to reward your pet with a healthy treat and plenty of praise after every step of this process. Soon, both you and your pet will look forward to the time you spend together during this important health care procedure.
The brush should be rotated in a circular fashion at a 45 degree angle with emphasis on the stroke away from the gingiva