Try to time and imagine when and where you will lock your legs. i.e. get out of the saddle and start leaning forward when your locking leg is up at 12 o clock, so by the time your leg reaches 9 of clock, your nuts will already be on the stem.
From there it's just a matter of resisting the crank, which should not be too hard because you should have already unweighed your back wheel by having your upper body directly above the handlebars.
Also try to focus more on leaning forward than locking your leg. As soon as you lean forward the farthest you can, locking your leg and skidding is a piece of cake.
When you do, it helps a little to pull up on the clips with your other leg too.
I've been trying to skid seated but still can't. The best I can do is get up halfway and lock, then sit back down, but that just looks stupid.
Anyone have advice on how to do that? or maybe wheelie/pedal backwards/360 wheelie spin?