Two local walking groups that I'd recommend, as well as the Ramblers.
Have walks every Sunday morning and in the Summer, some evenings. A really good group if you live in Norwich, don't have a car or don't want to use it, but want to walk further afield. They meet at Barn Road car park and share cars out to the walk start point – passengers paying a small contribution to driver.
Health Walks from Fit Together, part of Active Norfolk
These shorter walks are graded – from introductory of anything up to a mile; gentle walks of a mile or two for those who are new to being active or are returning from injury, illness or inactivity through to more challenging walks of 5 or 6 miles.
This website covers various areas in Norfolk. For the local stuff go to the Norwich Broadland and South Norfolk section and download the very detailed Central Walks programme.
If you are already an experienced walker how about volunteering with them?