My tips for making horror comics:
1. Consume lots of horror. As you do, think about what you think works or doesn't work. Okay that scene was scary... but why? The pacing? The monster? The build up? Even write down your thoughts about each piece of media you consume.

2. Read lots of comics and read lots of novels. Try to study anything that tells a good story, even if it's not horror. What I have found in my personal experience is that a good story and good context will amplify even the smallest scare. So don't skimp on good storytelling!!

3. Collect any comic or graphic novel that you love, the ones you think are just flawless or beautiful. Flip through them when you need inspiration! Reread them before you start drawing or thumbnailing, so you can sort of bone up on the visual language that you want to use.

4. Do studies of comics and specific panels that you really love. Just try to copy them or even trace them. It'll help you understand what is so cool about them. Here are some studies I did from the Akira manga. They are hideous but I learn by doing them. Also... my cat lol

Something that really helped me: drawing stuff that I know I will never show anybody. I'd say 80% of everything I draw is stuff I do not intend to show anyone, I'm just drawing to practice and to get better. I have tons of studies of comics I like, illustrations I find, etc

5. Remember that comics combines words AND graphics to tell a story, and therein lies the magic!!!! Comics can communicate in a special way that neither novels nor illustrations alone can!!!! COMICS!!!!