* Not keeping their dog on a leash.
This is a problem for many reasons. Dogs that are permitted to “run free” often get into accidents, or are aggressive to other dogs, or become the victim of aggression. They can also get into trash, to eat dangerous things like chicken bones. They can also ingest toxins.
Also, they can just plain wander off.
All of this can be prevented by keeping a dog within a fenced yard or on a leash.
For cats, allowing them to be outdoor pets is documented as decreasing their longevity.

* Not keeping a current ID tag on their pet, or embedding a microchip.
Many pets don’t have a current ID tag or microchip. These two items provide the BEST information so your lost pet can be returned to you.
Without identification, many pets can never be reunited with their owners, and are either put up for adoption or in more sad cases, euthanized because they are too old or deemed ‘unadoptable’ in some way.

*Skimping on nutrition, or feeding the wrong kind of food for its age.
A good quality food is important to dogs. Skimping on nutrition can lead to serious problems for puppies, and adult dogs. Dogs need a high quality balanced diet that is formulated to meet their life-stage needs, or breed issues. A single source protein, single source carbohydrate food will help avoid allergies as well. Find a dog that your dog likes and stick to it. Many brands offer coupons now, such as Hill’s Science Diet,
http://www.feedingisbelieving.com/believe/couponRegistrationForm.jsp
while others offer a club, where you buy a certain number of bags, and get a certain number free.