The trick is to measure accurately, but its a piece of cake. Here is what I did when I did it on my Sequoia that I owned. I took two pieces of paper and used doublesided tape to tape it to the spoiler. I poked holes in the paper where the screw holes need to be drilled in the door. I then positioned the spoiler on the car and measured to make sure I had the position correct. I then taped the paper to the vehicle. Then removed the spoiler from the paper and your drill holes will now be visible on the door. Drill the holes, remove the paper, now position and bolt the spoiler to the door.
You are done.