First different people use different system with underlying strength. Some people like Tesla can visualize a chair and the chair they visualize get's perceived by them the same way as a real chair. You don't get someone who doesn't think he can visualize pictures to that level of visualization ability by doing a few tricks.

In general you do something that triggers a reaction in someone. You observe the person and when she has the image or has the dialog you stop and tell the person to focus their attention on it. There are cases where that's enough.

There are also cases where a person has a real reason why they repress a certain way of perception. A person with a strong emotional trauma might have completely stopped relating to emotions within their body to escape the emotional pain. Then it's necessary for the person to become into a state where they are resourceful enough to face the pain so that they can process it.

A third layer would consist of different suggestion that it's possible to perceive something new. Both at a conscious level and on a deep metaphoric level.