Jeff Dunlap demonstrating the injection method:

Iowa Trapper demonstrating shooting for a heart shot with no injection required. I liked here how he waited until the skunk stretched out its leg before shooting for the heart:

Personal note (not best practices at all): I shot a skunk for the first time this year with a headshot. It didn't seem to have sprayed initially at all: but then about 10 minutes later the entire area started smelling. I don't know if it it did-spray or if it released the juices when it relaxed. The area smelled for three weeks.