It’s up to you! If your car surfaces, such as your dashboard and air vents, are harboring a lot of dust and debris, it’s a good idea to vacuum them first. This will help to remove any loose dirt and debris, making cleaning easier. Once that's done, you can wipe down surfaces with a microfiber cloth and a suitable interior cleaner.
However, if they just need a general dusting, there’s no reason why you can’t do this step first, allowing particles to fall to the floor so that you can vacuum them up later.