How can i style my leather skirt for a casual day out with friends?

All depends on what you do on your casual day out.

My first answer for your leather skirt on a casual day out is leave it in the closet. Now, a casual night out is a different story.

A casual day for me, includes activities that I would rather have shorts or pants on, not a skirt.

If it were me wearing the skirt a spiked choker, tank top, pyramid studded belt, wrist bands, wallet chain, striped stockings, and boots would be good. XD

I got to know that not to overdo anything! Keep things simple and classy by sticking to minimalistic style as less is often more when it comes to dressing up casually.

My fashion sense has stayed the same since 2005. XD

What color is it, how long is it? Very hard to answer.
Personally I wear leggings or pantyhose with a skirt, black or brown.
As for shirt, it depends. If it's cold wear a cute slightly oversized sweatshirt that matches the skirt in color, if it's warm wear a thin long sleeve shirt that ends where the skirt begins so there is no awkward lumpy overlapping, unless it's a skirt that tucking a shirt inside of would look good. A small, simple necklace. Done.

Hmm, depends. What's the color of the skirt? What's your hair color?