@Rob184 uh.. you could browse through CC forum and will find posts with similar topics and suggestions.
Some are: higher prices, no instant bookings, surveliance cameras and similar gadgets like wifi locks etc... be present on check in, take their photo ID and make a picture or photocopy of it... just don't forget to mention it in your house rules.
You could also set that only people with positive reviews from previous hosts can instant book but then you will lose all new users and there are a lot of them
Regarding internet you should put in your house rules something like: "It is forbidden any illegal behaviour including illegal internet download. The guest is responsible for any fees." As I've seen here on CC it should release you from any responsability.