Out of Tahoe city, we recommend the trail to Squaw Valley along the Truckee river on a designated bike trail – an easy three hour ride for any level of rider. Also the ride following the West Shore of Lake Tahoe to Sugar Pine point and back is also very popular among cyclists – again on a designated bike path.
In South Lake Tahoe, the ride form downtown to Camp Richardson is on a designated bike path and very popular with many quaint establishments to have a bite to eat or drink along the way.
Popular off road riding include the Tahoe Flume trail from Spooner Lake to Incline Village, or from the top of Mt. Rose to Sponner Lake, or all the way back to Incline Village. We also recommend the Fiber Board Trail which runs from Tahoe city to HWY 267 in Kings Beach, a combination of on and off road trails on a single car width fire road overlooking Lake Tahoe.
For more information on trails consult https://www.mtbproject.com, an excellent resource for novices and experts alike.