This is my favorite trail in Southern California because of the variety it offers. It is a mix of doubletrack and singletrack. Some parts of the trail has quite a bit of climbing, and some is fairly flat.
The easiest route is to take the Sulpher Springs/Cheeseboro Canyon Trail out as far as y ou want from the parking lot, and turn around when you get tired. Other trails may be short, but make sure you read the descriptions before you ride them. The Modello trail may be short, but there's a bit of climbing involved.
If you're looking for something a bit tougher, you can always take the Palo Comado Canyon trail, which has a significant amount of climbing.
Take 101 to Chesebro Rd. Yes, the road name is spelled differently than the trail name. Head north and take a right on Cheseboro Rd. You'll recognize it because this area says "Old Agoura Hills", and you'll see signs warning you to be careful of horses. Follow the very narrow street a mile, then take the first right before the Agoura Hills City Limit sign. You can park right here, but if you hit the parking lot during less crowded times, you're more likely to get something closer to the trailhead.
http://www.singletracks.com/item.php?c=1&i=874