So the chapter starts like this:
I continued to sip my coffee as he choked on his own blood. It was bitter - both the coffee and the look permanently etched onto his face.
I want to write a seamless description of a murder scene with what is written above, but I don’t know what to add next. How do I go about developing this scene so it is creepy and unsettling.
You say, "I don’t know what to add next."
I assume you have outlined your novel or at least the present scene and that you know what happens next. If not, step back and develop the plot in the usual manner.
I also assume you have developed your characters and know their motivations, goals, and stakes. If not, again step back and develop your characters.
Once you know what is going to happen, and once you know your characters, get into the mind of the viewpoint character and try and experience the situation from their perspective. Write down what "you" experience, what "you" would do, etc.
If you don't outline but discovery write, you do the same, except you don't know where you will be going and feel your way through the story from moment to moment. In that case, just follow your gut instinct (that will have been formed by a lot of reading in the genre you are writing). If you have no gut instinct, step back and read a lot.
Your aspiration to write "a seamless description" and to make the scene "creepy and unsettling", that is, the demand to write especially well, might put such a pressure to succeed on you that it stifles your creativity and blocks you.
In that case, follow this advice. Briefly: Allow yourself to learn to write and approach your first texts as exercises. Write regularly and consistently, as if you were training for a sport or learning a musical instrument. Be patient and persevere. Most authors need to write three books and gain some maturity before they will be published.
