Inside the package you'll find one .atn file containing multiple actions with the same effect, but for different kind of images. Some images may be too bright or too dark for the normal action, so you'll have to use one of the actions in order to make sure you get the effect you want.

First, don't use images that are incredibly dark or bright. Make sure your images have a normal amount of light and are not extremely dark. This way you can make sure your images will look good after adding the effect.

Second, make sure you use this action on new-opened images. Using this action on projects that already have other images in them may result in adding the effect to all the images. The reason for this is that I use a technique that lets you change the parameters of the effects in case you want, and because of that the effect may be added to every image on your projects if you use the action in that way. To avoid that, open a new image in Photoshop, use the action, save the image and then use it in another project.