Know your knives
The average writer is normally not someone prone to being a gun or knife nut. Sure, they might have a gun or two, they may have a kitchen drawer full of knives, but that doesn’t mean they know which one needs to be used in the scene where the zombies have just broken through the barrier erected by the pirates who were lucky to survive the assault of the purple ninjas. That means extra research. And ninjas.
Below is a handy graphic that covers a few of the basic blade types of knives. Obviously there are variations on these types and, of course, the difference between a serrated and plain edged blade.
Also check out this handy video:
Update: The knife aficionado from the above video has just produced a new information video that I felt was worth including. He goes into the blade types and what they are best used for and why. Very informative if you want to brush up on knives.