##1. Create a new layer above your artwork.

[![enter image description here][1]][1]

##2. Create a shape over the whole artboard (or the area you want the texture applied to).

##3. Apply your Grain (Effects → Texture → Grain).

[![enter image description here][2]][2]

##4. With your textured shape selected open the transparency palette and change the blending mode.

Different blending modes will have different results. I suggest starting with *Multiply*.

[![enter image description here][3]][3]

You can achieve the same effect by using a [textured image](https://www.google.co.uk/search?q=texture&tbm=isch).

If you only want the texture applied to a certain area just mask off the texture.

  [1]: https://i.sstatic.net/P7QMH.png
  [2]: https://i.sstatic.net/Yklmu.jpg
  [3]: https://i.sstatic.net/pO5ls.png