Cloudscape

To this day, there is no therapy specific for psychosis except for antipsychotics. A therapist can talk to a psychotic in the hopes that they will gain more insight in their own situation just like any other patient, but they can't give them any treatment which focuses particularly on psychosis.
Perhaps to this purpose, psychologists could subject the patient to a kind of training, a reality training. In such training, questions could be asked about a purely hypothetical person in a specific circumstance which relate to the patient's psychosis, such as:

"Person A finds that someone is following him or her. Is it more likely that:
A) the follower is involved in a governmental conspiracy, or
B) the follower wants to ask person A directions.

It may be useful to sketch the characters in the hypotheses as specifically as possible, so that, although they may be similar to the patient, the patient can think of them as other people. They do not have to be of the same age, sex, race, or personality. Important is that it is asked not what IS true, but what is more likely to be true. Implying that their delusions are false may make them defensive about their truth; they have to decide for themselves if they are true or false, but we can make them have a clearer view of their own situation by projecting it onto other people, so that they learn how others deal with them.
If one tries to convince a patient that their delusions are false by arguing about it, it is very possible that they will see one as being part of the conspiracy in their delusions. This probability is increased by the fact that many schizophrenics are often highly sensitive and might see criticism about their beliefs as a personal attack.
Because psychotics have a lot of imagination, they think highly parallel. They think in multiple possibilities, but are unable to see which is most relevant. They see so many possibilities in their mind that they no longer see which are likely to happen in reality and which are not.
Most people will tell psychotics that their delusions are impossible. In fact, nothing is impossible: it is always possible that they are being followed by someone who is involved in some conspiracy, but it's just very unlikely. Because psychotics are so good in hypothesizing, when they are told that something is impossible, they will eventually realize that this isn't true. "What if my father had somehow gained access to top secret information without my knowing and is keeping it somewhere, what if the FBI is pursuing me for this?" What often happens then is that when the psychotic realizes that their delusions are, after all, a possibility, they will wonder why whoever is telling them that they are impossible is "deceiving" them, which might make them believe that they as well are involved in some conspiracy which is meant to keep them from knowing the truth. Instead, it is better to tell them that their delusions, while possible, are very unlikely.
To a schizophrenic, the relevant possibility is no longer the most probable one, but the most drastic one. Because of their high faculties of imagination, they will also be able to imagine all possibilities very vividly; what then matters to them most is those imagined possibilities which elicit most emotion when they imagine them, that is to say, those which they fear or hope for the most. It doesn't seem to matter how likely they are because in their minds, they are already real: they happen in their fantasy as vividly as a dream happens in our own.

"Its astonishing in the Inner Worlds - the Innerverse..."
— Silvis Rivers, schizophrenic artist

Teachers of enlightenment will tell you to live in the here and now, and for this reason meditation will often focus on sensations, especially physical sensations such as breathing -- yet, this omits part of the here and now. For it is a mistake to think that everything that happens inside one's head, that is, one's thoughts and fantasies, is not part of the here and now.
Consciousness is comprised of two parts; the outside world and the world within - the "innerverse." However, there is no clear line between the two. They are not as such distinct, except in that one cannot affect the other unless you let it.
The innerverse, however, is by far the most complex part of our lives. Our mindscape varies constantly, much faster than our physical environment. Thoughts shoot through our heads all day, and for many people with a vivid imagination, the same counts for daydreams. Some schizophrenics know little else beyond their inner world, which is why they can live detached from the "real" world -- this may make them seem unemotional, but when something happens in their inner world, they can react highly emotionally to that: in this way they may feel as much affection for imaginary friends as other people do for real friends, while feeling little affection for real friends.
It may be important that we learn to control our inner world at least as well as our outside world. After all, how we feel depends on the former rather than on the latter. Meditation can help us become more aware of our sensations - what happens in our outer world - while hypnosis can help us become more aware of our imaginations - what happens in our inner world.
Through visualization, we can not only become more hopeful about those things we'd like to see come true, but they will also in themselves make them come true in a way -- in our (day)dreams.
There will be a day that schizophrenics will be seen as true geniuses. Over the past centuries, the innerverse has become more and more important because of art, which is basically an expression of our inner world! Music, books, poetry, movies, videogames, even science -- anything that is notional is part of our noosphere, which is basically our collective innerverse. These things become more and more dominant in our lives, especially as we slowly come closer and closer to achieving immersive virtual realities.
The Innerverse has something divine: because we are the Gods of our own inner worlds. We are almighty over our fantasy, at least the amount of fantasy we do have. The nature of our world will more and more become like that of our innerverse, until our entire universe has become like one big dream. One day science and fantasy will meet: everything we can imagine will be real, for anything we be able to conceive of, we will be able to create.

See also:
Love of Beauty