I love denim skirts! It's all about the proportions, to me.
If you wear a straight cut mini, perhaps wear something looser fit on top - slouchy button down shirt, flowy blouse, chunky knit. I think this evens out the silhouette so that we don't look tubular. This especially applies to a pencil style skirt, and if above the knee always seems to work better in a darker wash.
I also love denim A-line, my fave is an old one from Oasis. This lies flat to the waist instead of being the traditional button/zip fly arrangement. I would actually try to avoid a front fastening skirt, I think they can frump/bunch up in this area regardless our figure.
I wear the a-line with tighter fit tops, black lace and white go really well with it as the denim is a lovely dark indigo. Anything seems to go with this skirt and I am quite sure it is the most versatile piece in my wardrobe. Jumpers, shirts, tees, etc. One thing to avoid with a knee length a-line is don't make your tops too flowy, and if the skirt is knee length keep your tops no longer than the waist or it throws things off proportionally.
I wear my shorter denim skirt with flat or low heel shoes and the longer a-line with anything (boots, heels, etc).