You need to shop for Pet Insurance in the same way as car or home insurance - work out what you want covered, and then find a policy that suits you best
In general, there are two forms of policy - those that cover the cost of each condition
for 12 months (up to a maximum amount), and those that cover the cost of each condition
for life, up to a maximum cost. The latter are more expensive that the former - but if your dog is diagnoses with epilepsy, or diabetes, for instance, then 12 months worth of cover means that you might be paying out for expensive medication for several years with no insurance to cover the cost
Other things to consider are the cost of a behaviourist, alternative therapy, dental work (many policies exclude it) and the extras such as kennel costs if a family member is taken to hospital, for instance
Enjoy!