Immersion. The fastest way to get through the "practice hump" is to accept the dip in productivity and keep learning. No turning back to your old method. The same applied when I learned the Dvorak keyboard layout, and I presume the same applies for language learning among other examples.

For vim specifically, I think mode changes are the most important to learn first. Past that, it's building muscle memory for all the keybinds (and actually discovering the keybinds).