The first thing you may need to do is buy a net for the trampoline and establish rules and guidelines for use. You should also call your agent and make sure your insurance company does not have any restrictions for having a trampoline; this can vary by carrier. Another way you can protect yourself and your family is to also place your netted trampoline in a fenced-in yard to prevent unauthorized entry by neighbors.
I would also recommend making sure you have adequate liability coverage and look into adding an umbrella for additional coverage. In the event of a lawsuit – if a non-family member is injured on the trampoline – an umbrella can provide extra protection.