when i'm teaching people this stuff i like to stress how much weight distribution has to do with it. try this: pedal around somewhere open, slowly. keey your hands on the bars and really lean forward, so that your legs are behind you and most of your weight is on the bars. keep pedaling, but play with fore and back pressure on the pedals - by pulling up with your forward foot and pushing with your rear foot you should be able to jerk the drivetrain backwards for a second. don't try to hold it or skid - you shouldn't be going fast enough for that - just drag it backwards for a split second.

get comfortable doing that. it's not what you'd use while in the street or riding, but once you're comfortable putting your weight on your bars, you can do anything with your rear wheel - you can hop it a little bit if you need to, you can skip and skid.

quite frankly, i recommend 'skipping' as short skids - the wheel doesn't need to leave the ground. just give yourself a little hop while pushing one pedal and lifting the other, and as you're coming back down (all w/i a fraction of a second), resume pedaling.

as always, practice on wet grass or wet pavement for added effect.

step one is getting comfortable with the mechanics
step two is getting comfortable using these moves in the street
they are two different things.