Part of this is a timing thing. you want to try to lock legs before you actually want them to lock. You should end up locking legs with your cranks more or less level (9 and 3 oclock) but need to start resisting sooner than that. For me, it worked to think "lock up" when my front foot (which would become the back foot) was around 5 oclock. Dominant leg back works best for most people. Pull up on the front foot, too, can't emphasize that enough.

The thing that's a b* is that if you "miss" and don't get it locked up, you better right away get back to pedaling or the bike is gonna throw you around a lot. Be willing to pedal if you miss.

What complicates it is having to move your body weight forward (at first, til you get more leg strength and can just pop off the saddle a bit to skid). All those movements (lock up, throw weight forward, did I get it, oh crap I have to keep pedaling nuts-to-stem??) is a real trick.

It really is true that the faster you go, the easier it is, but that puts a premium on being able to lock up at a higher cadence (tho on 48x16 you could be going "fast enough" on a slow cadence if you hump the stem). The faster you pedal, the sooner you have to think about locking up (say, 3 oclock on your future-back-foot, instead of 5)

It will eventually become second nature after a WHILE.

Learn to skip first, I cannot emphasize that enough if you are actually trying to slow down.