You'll see a mailbox/check-in station for hunters on the left and the trail itself skirting outside the fence along the roadway. Soon after it starts, the trail forks. Take the upper trail if you're headed for the ridge. Take the lower trail down into the valley for a short one hour loop hike.
Waimano is in remarkable condition: it's wide, level, and easy to traverse. Much of lower section of the trail follows a manmade ditch for water. I also remember short water tunnels (these look like caves) at various points along the route.
Although lengthy (15 miles round trip), the Waimano Ridge Trail can be completed in a day since it is graded and devoid of any major obstacles that may slow your progess (I've even heard that mountain bikers can ride a goodly portion of the trail to the top and back).
The view into Waihee Valley from the summit saddle is beautiful and if you're into adventure, you can head left along the Koolau spine for a traverse to the topping-out point of the Manana Trail. Fellow hiker Wing Ng even headed right and had a memorable descent of Waiau Ridge.