I didn't follow any tutorial. It's not hard, though - just do as I mentioned with the Mixer Brush Tool.
Make a transparent layer over the original image (I'd suggest upsampling it some), then call up the Mixer Brush Tool, choose a bristle brush, and set it to Sample All Layers. Fool with the settings until it mixes for you in a way that you can make nice smooth strokes over the original. You'll be picking up color from the photo underneath and smearing it around on the top layer. If part of it doesn't come out the way you like, just erase it. Don't set up to use too many bristles; the object isn't smooth perfection, but to show some strokes.
Here's just a few minutes work with the technique...
When you're all done you can do things to accentuate the brush strokes, such as create another layer and run the Filter - Stylize - Emboss tool, then set the layer mode to Overlay blending. This gives the image some texture...
The only way to really get to know the Mixer Brush is to experiment with it. Find settings that allow you to do what you want easily. Fool with it until it yields!
Have fun!
-Noel