Welcome!
I've been riding Edmonton for many years, but I've only started to take it seriously since last year.
Terwilligar Park is a good place to ride. Watch out for dog walkers on the main trails. Mill Creek Park and Ravine are excellent, too.
There are miles of singletrack and multiuse trails up and down the River Valley. LBS rides sound like a great way to get yourself acquainted with the trails here. Pick up one of the Cycle Edmonton maps. A LBS should have one.
Supposedly Fort Saskatchewan has the best stuff around here, but I haven't tried those trails yet.