6. Pet's treatment determination, choose a plan that doesn't limit your choices with a confusing fee schedule, or benefit schedule
7. Pre-existing condition, meaning those that existed before the original policy effective date, whether or not they were previously diagnosed or treated. These may include the congenital conditions your pet is born with such as patellar luxation, entropion, ectropion and liver shunt. Make sure the policy you choose clearly states what is and is not covered in a way that is easy to understand
8. Lifetime continous coverage, it is important to know that your pet insurance plan will continue to help treat the problem from one policy term to the next.
9. Veterinarian recommendation, they must have have heard all the news, good and bad, from other policy holders. Ask which one they recommend.
10. Experience expectation, when you have a problem, or you need help with a claim, a pet insurance company who employs pet lovers who care, and who understand pets, can make all the difference.
source:
http://www.petsbest.com/TenThingsYouShouldKnow.aspx