I've spent the last year, approximately, writing serial-killery violence for my novel, "Dear Killer." As I went along, I learned a few things about writing the morbid and vicious; here they are.
1. Only write violence when you need to.
Don't overindulge. When you can leave something to the imagination, then leave it to the imagination. If you start adding too much blood, broken bones, bruises, exc., then it's all going to blend together in the reader's mind. Also, it's going to get really gross. Each act of violence that you describe should have a point. It might be to introduce the violent nature of a particular character, perhaps, or to shock the reader into paying close attention to what comes next. You don't need to describe every gruesome bit. The reader will get the point. Just choose the most important pieces of blood and gore, and describe those thoroughly.
2. Use action words.
No, I don't mean "verbs." "Action words," as I think of them, are a subset of verbs. They are verbs that denote intense action--for example, "crushed," "sprinted," "slammed," or "shattered." Verbs that are not action words, on the other hand, are "broke," "cried," or "kicked." Action words, the kind that you would use in extremely violent scenes, are the kind of words that make you cringe when you think of them happening to you. You don't want the word "shattered" having anything to do with you, though you might be okay with "kicked." Basically, though you might not want to do this in every scene, always go for the extreme when you write violence. Make sure it's remembered.
3. Focus on details.
This is a general writing tip, really, but focus on the little things. It is far better to "zoom in" on one or two specific details than to explain the whole scene. It gives the reader points to sort of anchor themselves with. Describe the color of the sky and the look in the murdered person's eyes, but nothing else, for example. The reader doesn't need to know what absolutely everything looks like, because they won't remember it all. If you only describe one or two things that are very indicative of the moment, it will be easier to picture; the reader will sort of realize that those things are "important" and should be paid attention to because there isn't anything else to pay attention to. It makes the scene more memorable. And, of course, to repeat what I said before, your violence should definitely be remembered.
4. Know what you're talking about.
This one is going to make you a bit uncomfortable and make your search history a bit questionable. But, basically, you should understand what you're writing about. This may seem self-explanatory, but, really, you should google things far beyond what you want or think you need to google. Like, what sound happens when you stab someone. Or what it feels like to have your ribs broken, in detail. Ick, I know. Gross. You're not going to want to google that. But you should. Strive for obsessive levels of accuracy; it just feels more real that way.
Of course, in the end, these rules are really only guidelines. And rules are meant to be broken, anyway. Good luck with the gore!