Patience and a lot of prep work. Here's a link that will tell you more. And, before doing the black, make sure you really like it, as it will be hard to go back to a lighter color later.
the easiest way is to sand down the edges of the piece (randomly so it looks natural). You can also randomly scuff doors, top, etc. Then rub the sanded edges with a wax candle. When you paint it black, the paint won't stick to the wax. Then you can put other dents in it to your liking. Another cool look is to paint a color underneath the black, like red or dark green, instead of sanding through. Then you have a black cabinet with red highlights instead of "natural." Good luck! It'll be easy!