There’s not much out there tbh. Just make sure your bike is well locked up and out of sight when in Yarmouth.
As mentioned head into Norwich for a play at Mousehold which has a few fun little lines. Or head a bit further out to Bacton – which has more to offer. Or, if you’ve got time head futher north out towards Sherringham and ‘pretty corner’ – some fun little bits of singletrack out there.
Although, if you’re in Yarmouth, you could always think about doing the Werrymans Way path (http://www.wherrymansway.net/wherrymansmap.pdf) which starts at the back of Asda, and goes all the way to Norwich. It has a few little pub stops on the way, and then you can get the train back to Yarmouth for about £4. The train station is right beside Asda where the route starts.