How much it costs every month
Whether pre-existing conditions are covered. If a pet was already diagnosed, will the insurance cover the bills for this condition?
If you want preventative medicine covered (or how much you want covered)
What are the limitations of the insurance? Are there yearly limits? Some plans have lifetime limits.
Whether a percentage of the bill or a dollar amount will be reimbursed.
Whether congenital and hereditary conditions are covered. These include hip dysplasia, heart defects, and similar problems.