urm.. if anyone could explain the 'steps' from turning a child painter into a leonardo da vinci.. i think he'd be making quite a name right now.

anyway, there isn't a shortcut or an easy step-by-step tutorial to teach you how to turn a hand drawn drawing/sketch into something like the example you gave.

it is however possible to first learn the basics of Photoshop to create a 'dumbed-down' version then later progress on yourself via experimentation to find your own style and preference that would simulate the results you're looking for.

So my suggestion is:
Learn the Lasso and Pen tools well. Then discover gradients and finally, learn to control brushes.

that's my easy steps of getting what you'd want.