Molgrips, as iainc said, if you get on the GMBC club page there are plenty of rides locally and with it coming into summer we’ll probably have some evening rides away. Some of us that don’t live in the Milngavie area have been doing some exploration out other ways, too.
As others have said, maps are useful but won’t have all the trails marked. I’m sure if you head out of the city in any direction and follow your nose you’ll find something worth riding though, and if you want to ride out of the city rather than take the train, the canal and things give some options to avoid the traffic.
There’s a lot of road biking in the area too, heading in the general direction of Stirling gives good options (if you’re going to Stirling, get to Kilsyth, go over the Tak me Doon, and go straight on at Carron Bridge – super easy navigation).