I have built / rebuilt / reshaped / maintained woods trails for several years now. My neighbor has about 15 lineal miles of trails in his wooded property. He builds the trails for several uses: initially for woodlot management, to access harvestable logs for firewood and lumber (he saws and dries). Also, he and his family hunt, so access trails allow easier movement thru the woods and somewhat encourage the flow of wildlife in certain areas. Also, he is an avid ATV rider, so woods trails are very desireable. I am also an ATV rider, so that's my interest.
Years ago, he'd grub out the trails without thought to the waterflow and erosion and so the trails would need periodic rebuild. His tool was a tractor backhoe. He backs up to where he wants the trail to travel, and grubs a flat area. Then he backs up onto the flattened area, and starts again. He's made trails up hils and areas using this technique that you would not believe we'd even attempt. A few years ago, I got involved and gradually built up two landscape rakes (one for him, one for myself) to use behind our compact tractors for trail shaping and maintenance. I read online somewhere about sloping the trails to encourage the water to flow straight across where necessary, and adding waterbreaks to get the water to stop flowing downhill in the trail, etc. My neighbor and I started using these techniques and instantly the trails became stable and lower maintenance. For instance, there was one trail that was bad because the water washed straight down the trail. I put 7 waterbreaks in there one day, in the span of 300 feet of trail. Erosion stopped immediately and even though that trail gets atv traffic there is grass growing on it now. These days, if he makes a new trail, I generally follow him imediately with the rake , giving it the desired final shape and slope.
At first the waterbreaks I put in seemed to be too high, but of course they settled and we also got used to them and afterwhile they make sense.
My technique is to use the landscape rake, tilt it so water will run off the lower edge of the trail, and where it makes sense with the surrounding terrain (like where there is a supply of water flowing onto the trail from the uphill side), just below that point, I lift the rake and deposit the soil and rock I have gathered into a row generally straight across the trail. The amount of deposited material varies but is generally about as much as the rake will drag. After raising the rake to deposit, I then back up the tractor far enough to use the front tractor wheels to pack the entire row width. Back and forth I drive, packing the row of soil, steering left and right to get it all. Later it settles about a third, so if it seems to big at first, don't sweat it too much. The action of driving over it makes it have a nice shape for atv/walking traffic, not too sharp at the bottom or top.
The whole grooming game is based on fixing what is broken. You fix up the worst problems, and then study the results. Nature will teach you the rest.
Here are some pics...