The following diagram gives a simple example of what I try to accomplish.
|Black to move|
I tried to solve this first in my usual trial and error mode, but with that I didn't came very far.
But when I focussed on the covered squares, the invisible cage the king is in becomes slowly visible. And then the moves are easy to find. I take my time to develop a better square vision.
Renko's ICT 2 provides exactly the right kind of exercises that can be used to develop square vision.