Bob vomited, covering the person next to him in chunky bile.
This is a good sentence in its own right, even including a bit of gore. But I could picture it in a romance novel.
However, any sentence can have a change in perspective and setting which may change the tone of your book. Bob vomited, a foul black liquid shooting from his mouth. The noxious smell emanating from the liquid caused stomachs to turn, as it covered the person next to him in chunky bile. Much more suitable for a horror than a romance, and I believe it illustrates the difference in gore between genres.
First off, there is no wrong way to do gore. The bloody pus-oozing liquids of life are ever present. That even counts in romance, a jealous lover stabbing another needs to be realistic.
Write for your audience - Write for the story
Remember what I said about the romance book? If you want to be successful in the romance genre, your orgies cannot constantly turn into blood orgies (Although that may be a good book idea). Not to say that the two don't mix, I'm sure there would be plenty of time for gore in any jealous quarrels, but that isn't the main focus of your story. Having too much gore, or even details in the gore could drive away the core audience you are seeking. It's not impossible to write a bloody love story, but it might not connect with your core audience the way you expect.
However in an action-packed thriller, there must be some blood, and it will be much more integral to the plot. If your character is scarred horrifically in a scene, you need to convey the desperation your character will feel. The color, the smell, all of it adds to their story. The reaction to the blood is half the story, setting the tone for the shocking wounds. It also gives you a chance to let the character’s personality shine through, especially if they are afraid of blood.
In splatterfest stories, the gore is the main attraction. The audience prefers hardcore, off the wall deaths full of blood and pain. It has to be a little (a lot) dark and blood has to cover every wall at some point. You won't be successful if you try to sell a splatterfest with romance gore, the same as splatterfest style detracts from your romance.
Real experience matters
I have an advantage when it comes to writing gore. Not only did I grow up imbibing horror movies and books, watching the monsters paint the walls red with blood, but I worked in the medical field. You see a lot of blood when you work with nurses. I really believe this up close and personal look at our bodies has made writing gore that much easier. We are nothing but bags of meat and liquid, and having a front row seat to blood, it becomes easier to talk and write about.
I know the different types of puking, and how the liquid spreads across the floor. I've seen an artery get nicked, and have watched the blood squirt across the room with a man’s heartbeat. When you've seen it every day for years, it becomes second nature for you to think about it.
YouTube is a powerful tool as well, I'm sure with a short search you can find videos of real blood to study. Pimple popping videos are also fantastic for helping to introduce you to the kind of grossness our bodies are capable of producing.
Absurdity can be the name of the game
Exactly what it says. Some of my favorite death scenes are over the top. They're my favorite exactly because they are so dramatically exaggerated.
While I know that a heart pumps blood, there's something about watching a steady fountain of it shower an antagonist that sends a chill of pleasure up my spine. I know it's impossible for the human body to hold that much liquid, but it sure is fun to read. Absurdity can be a great boon to your gore writing, turning a normal scene of death and blood into a masterful stroke of drama and fear. If the story calls for it, don't be afraid to use buckets of blood and vomit to get your point across.
Color matters and smells matter
Like with a lot of things in life, color matters. Especially after years in the medical field. Black, red, yellow, orange, dark noxious green, these are the colors your body puts out when trauma happens.
Say you have a character vomiting. Setting the mood for the scene is important. After all, Bob has to do something now.
These are just a few simple tips to write gore. Hopefully, you have found it informative and you are ready to tackle that bloody part of the story.