I just installed 'brand new' headlights
What product can I use on new headlights, to prevent future fading & yellowing & keep them clear?

 

Shade.


Rain-X Plastic Water Repellent works to keep crud off for better visibility, but long term sun exposure is a killer.

 

or a garage...which even i dont have so

 

I had the headlights on my Corvette covered in PPF, (paint protection film), made by Xpel. It will protect from the sun's UV rays and prevent light abrasive scratching. You can do it yourself or have it done relatively inexpensively.
https://www.xpel.com/products/headlight-protection-film

 

New lens keep them clean-> Meguiar's makes a product to protect: