Proof that fashion never gets old are denim skirts. They were thing back in '70s. In '90s they got a big comeback and here they are! Better than ever. You can wear them for any occasion. There is variety of styles, so we got pencil denim skirt, flared, classic biker design, A line denim skirt and many more. You won't have a trouble finding yourself a perfect one. 
As for the length, you can find it in every possible one. From mini, midi to maxi. Yes, there are some maxi denim skirts. They are trikiest to style!

Good thing with denim skirts is that you can wear them for all ocassions. From everyday to special occasions.
For casual style you can go with a classic tea, striped blouse and biker jacket. For more fancy one you can go with floral print, silk blouse or ruffles. You can style it with pair of sneakers, flats or heeled sandals.
For perfect summer look, my vote would go for off shoulder tops, blouses and ruffles. They are effortless, chic and cool. For more chilled look you can go with graphic tees and kicks. You can never go wrong with it.
If you don't own denim skirt, make sure to check out closet of your mom or grandmother. I'm sure you find a few timeless pieces. This one I found in closet of my mom and I love it. It's a pencil denim skirt, with a twist. It has a slit at the front and at the back there is a zip all the way down.

Denim skirts are the best choice for situations when you don't know what to wear or you are in a hurry and don't have much time to think.
Let me know in the comments do you wear them and what is your favourite way to style them?