Mainly, I think you practice like you would any skill, controlling motivation, repetition, difficulty, etc. I would be very surprised if sustained training yielded no improvement.
I know I've read books on it before. Never applied myself for any length of time, so can't give a fair assessment.
And for your own training, I don't think 2 was the right thing. That might help you to hold an image, but I don't see it helping you generate the image to hold. 3 doesn't look helpful either - I don't think logicking it out would help.
And even 1 is questionable, as you're trying to maintain pieces of a sleep state. That might allow you to visualize if you can pull it off generating enough of a sleep state.
Try to do colors. Then basic shapes. Try eyes open, eyes closed. I find it easier to in the basic Matrix white space. Try to get a 3d image, instead of 2d. Maybe simple isn't the right way. Maybe a natural scene with detail is easier. And also, see about adding other sensory modalities. I'm probably best at "visualizing" sound.
A lot of dance and movement theorists recommend "visualizing" body movement as well.
Basically, you're just learning how to control and train your nervous system, so I think a lot of movement theory would transfer. I wonder if Feldenkrais ever had anything to say on visual visualization. He's very good on movement and learning theories.
I will try colors and natural scenes and (like Elithrion suggested) familiar full-featured scenes.
Other senses don't transfer, that I know. I have good aural and motor "visualization".
Edit: I didn't get colors to work at all. Real scenes, especially familiar ones, and scenes that were emotionally strong, yielded some results. I got to something like 3.75 on the scale (close to vague and dim but on the way to moderately clear and vivid) for lots of locations that I visit/see regularly. When I noticed that I was better-than-4 on lots of things, I t...
Previously: Generalizing From One Example
Summary: I do not have visual mental imagery. I want it. How do I get it? What exercises, if any, will help?
In further detail... Here's Francis Galton's Statistics of Mental Imagery paper. I'm not quite at the 3% level of completely unable to form mental images, but I'm close. In particular there are three times I have vivid, sharp mental imagery, and the existence of such times tells me I have the brain hardware to visualize. It's enough to let me know that I want it all the time. Unfortunately I don't know how to get it. And searching online has proven difficult and frustrating... for example this article is first of all about a different meaning of "visualize", it's talking about some kind of self-help motivational thingy, and second of all it starts by saying "How to Visualize: I want you to relax and close your eyes. Picture a hot, sunny day at the beach."
Full Stop. Halt, Catch Fire and Burn.
That's already too far. For those of us who don't visualize, practice definitely does not consist of pulling up mental images, playing with them in new ways, and expanding our imagination. I'm very good at imagination in some ways, but I lack that first ability to pull up a mental image. That's what I want to learn how to have!
Here is a description of what I can do, what I have tried, what I have learned, etc.
I see vivid visual mental imagery in 3 situations: