Here are some good suggestions from a post I found :
1. Wipe the lens and foam using a microfiber cloth, the same kind you would use to clean glasses or a computer screen. Dab the cloth into water or soapy water, when necessary. Even better get one of our waterproof VR Cover that is easier to clean.
2. We recommend you wipe our waterproof VR Cover with nonalcoholic antibacterial wipes after every use and use alcoholic wipes just every 10 – 15 users. The residue from alcoholic wipes can be a bit harsh on some people’s skin.
3. Use watch glass protectors or some other form of plastic to cover the lenses. This can help to prevent scratches.
4. Keep your VR headset somewhere where it won’t collect dust, use a can of compressed air to blow it out of any nooks and crannies.
You can read the full post here, hope it helps