Your Oculus Rift came with a nice little cleaning cloth to wipe the lenses. As soon as you put on your Oculus Rift, 30 seconds later the lenses are covered in some face slime and if the weather is not perfect they're probably fogged up too.
I cannot help with your face slime. However the fogging I can provide a simple solution. Oculus CTO John Carmack even swears by this method.
Just wipe the eye-facing sides of both lenses before you put the headset on and kiss goodbye to VR fog. This method will work on any Virtual Reality device such as the Oculus Rift, Gear VR, Google Cardboard etc.
Purchase Clarity Defog It Anti-fog 3 Dry Reusable Wipes (Not being paid for this)