It depends what your interests are.
If you wear an anorak & woollie hat, clutch a thermos of tea, a note book & pen and hang around train stations, you are bound to meet others with similar tastes.
Other suggestions are
Night school
Sports clubs
Pubs
Exercise classes
Your local library will have a list of all the organisations in your ares.
Good luck.
Join a gym
If you're interested in real ale then join your local branch of CamRa
Dance classes (good way to meet the ladies!)
Join a football or rugby team
Join the local supporters club of whichever football club you support