Understood

I mold my chakra in my body and release it through my hand, my chakra would travel through the air toward you, when my chakra come in contact with you, it would travel up to your eye region and begin to alter your sense of sight, I do all of that without giving you a clue of what I had done. Now am set.
I begin by making a hand seal then I bring out a kunai from my bag with my free hand and thrown it at you, as I release the kunai, i manipulate your vision with my existing chakra in your eye region making you see an illusion where I form a clone and it run towards you. I would make sure the clone match the movement of the kunai so that it can be presume real by you.
Deduce it a illusion illusions don't produce shadow when hit by light, so I would take notice of that and know the clone is not real.
Another way would be do to throw a kunai at the clone, since it is a illusion the kunai would pass through the clone.
Way to counter when I find out it is a genjutsu I would distort my chakra flow for a moment which would make the clone disappear allowing me see to the real weapon of destruction, I would counter the kunai with another kunai to avoid wasting my jutsu slot.
Or I could treat the clone as the real thing and go for a wide range attack like Wind Release: Great Break Through which would take out the clone and its master. It like killing two bird with one stone.