It's pretty impossible to say from something sketchy like that. Show us something more refined. At least tell us what you're trying to do with your piece. I can't tell if he's supposed to be cartoony or realistic. Can't tell if he's supposed to be silly or bad ass. I'll still give it a shot:
Is he riding a tiny horse and is his body going through the horse's back? Even if you're working on a cropped area of an image you need to think about these things. How would the riders body interact with the animal etc.
Where the heck is your light source? You should have this figured out before you even start shading.
Your skulls look pretty bad. They don't seem stylized but they don't look realistic either. Just looks like you're doing skulls without knowing how skulls look. I did a quick over painting to the guy's face but I'll leave the shoulder skull up to you. I couldn't tell if he was supposed to be wearing a mask or not but that's none of my business.
My main piece of advice: Get some fucking reference! Get a ton of reference of guys on horses. Get reference of knights, armor, skulls, swords etc. There's no shame in doing that. When you do work from reference and you'll retain that shit in your brainbox and you can do shit like this from imagination later.
Hope this helped.