At the mill, the trail head is well marked with a sign across the street from the parking lot. On Riffle Ford Road, you need to travel south on the road to see the sign at the trail head there on the opposite side of the road from the parking field.
Once you are on the trail, it is well marked with red blazes and metal posts every so often. There are one or two intersections, but sticking with the well traveled path will keep you on the Ridge Trail.
Overall, it is a fun trail, with plenty of good climbs and downhills. There are a fair share of at grade creek crossings to splash through as well as a few nicely put together bridges. There are nice pump sections created by the natural layout of the area and a few fallen trees that can be climbed over. The trail, as a whole, does not have a lot of technical features, but the rolling dips, long climbs, at grade crossings and switchbacks make it a very fun trail to ride.
GPS data logging gave an vertical climb over 1000' or so. I can't remember the exact number at this time, but despite the relatively even start/finish height, there are plenty of hills to climb and zip down.
It should be noted that this trail runs through managed hunting acreage. Luckily it is bow hunting only and not rifle, but still, care should be taken during prime hunting season to avoid issues with hunters. Wear hunting orange, maybe put a bell on your bike, make fewer deer noises while on the trail, and be courteous to the hunters in hopes that they will do the same in return. More information about can be found at the link below.