Filtering

Can anyone suggest any tutorials for filtering? Ideally, I'd like to (one day) be able to make things like this person has done. I don't have any real knowledge of filtering, to be honest, but I know a lot about Photoshop; I used Photoshop CS and have familiarised myself with it; I know it at the back of my hand.

I need to start from the basics, but I would like to be as advanced as the artist who's link I have posted above. Does anyone know of any tutorials or techniques that work?

Thanks in advance!