So, I'm assuming your issue is making sure that the character's death has impact on the player, and makes them actually feel something. If that's it, I'll try to help the best I can with a few tips.
Sometimes, characters like these are far harder to write than your main ones. Your main ones have an entire story to tell the readers who they are, so even the blandest of people will develop. With these early death characters, you have to let us know and feel attached to this character quickly.
Try give give them at least a few scenes with a bit of focus before you kill them off, and make sure their personality shines through. If you can, try write down a description of what you think the character's like, and make sure he actually is a character rather than just a plot device. Whether he's optimistic, funny and clumsy or dark, serious and professional, make sure that you're writing a character and a death rather than just a motivation for the main character.
Also, try avoid making it too obvious he's going to die. Because in loads of works, there's clearly a character that exists purely to be killed off, and no one is surprised when he finally is.