I keep them on my shelf away from natural or artificial light and I wrap them individually in plastic to preserve that new smell. It's a hassle, sure, but I love my stuff looking new.
With the large volume of books now in my collection I no longer have easy access to them. They are stored in long white boxes in a cool dark area of the house. However I do love some of the covers and have resorted to a cheat in order to display them. Using the Grand Comics Database I print out the covers I like and display them in 8x10 frames on the wall. I usually do some retouching in photoshop to bump up the colors and deepen the blacks. Now my real covers stay protected and I dont care if sunlight or whatever gets on the ones on display.
Ikea frames are $2 ea and are perfect for the books for display. I have my entire collection room lined with books in a row at the top. I use mylar, silver age bags and boards with the comic. For all other books not on display they are all bagged and boarded and put in short comic boxes.