This trail system is a great place to start with mountain biking. Most of the trails are wide, with plenty of room to maneuver. You will be sharing the trails with hikers, dog walkers and others out enjoying the park, but there is plenty of room to go around them.
But while the trails are wide, the hills can be killer. Relatively steep and decent in length, they really work the legs and cardiovascular system out. Work your way south to the open section of Blue Heron Trail and you'll be rewarded with a quick, straight downhill section and lovely view of the lake.
When you're ready to give some singletrack a try, head to the Gude Trail and Parilla Path trails at the south end of Westside Trail. These are a decent representation of a vast majority of the trails in the Montgomery County area. If you can handle these two paths, you should be able to tackle much of any trail out there that is rated as a Blue Square.
Lake Needwood Trails are a great place for beginners or people who think they might be interested in trail riding to start. The trails are easy to navigate, but provide a decent challenge to anyone willing to give them a shot.