From the Massie Gap parking lot take the rhododendron trail until you reach the white blazed Appalachian Trail. Take the AT towards Rhododendron Gap and enjoy the breathtaking views. Then keep following the AT past the Thomas Knob shelter to the Mount Rogers spur trail. Follow this trail as it ascends into thick woods to the summit.
Note:
To catch the beautiful blooming rhododendrons at Rhododendron Gap you need to hike around early/mid-June. It's a hit and miss game to catch them at the right time.