What are the conditions for a dream to be considered true?
In the Name of Allah, the Most Gracious, the Most Merciful.
As-salāmu ‘alaykum wa-rahmatullāhi wa-barakātuh.
The science of interpreting dreams is a rather difficult and intricate field that requires one to have in depth knowledge of the different sciences of Dīn. Generally, dreams do not materialise in reality as exactly seen in one’s sleep. They tend to hold a hidden meaning which needs correct interpretation in light of the Qur’ān and Hadīth. This is why it is not everybody’s job to interpret dreams.
The mere knowledge of the different factors that indicate towards the truth of a dream is not sufficient for one to interpret a dream.
Hereunder are a few conditions that one should fulfil before attempting interpretation of dreams:
Should be knowledgeable regarding the Qur’ān and Hadīth.
Should have an insight in the linguistics of the Arabic language.
Should understand the conditions and temperaments of the people seeking an interpretation.
Should be knowledgeable regarding the principles of interpreting dreams.
Should be spiritually upright and have good character.
Should be truthful.
May need to take into consideration the present conditions.
Further, not all dreams hold a message and thus cannot be interpreted. Rasulullāh Sallallāhu ‘Alayhi Wa Sallam said:
“Dreams are of three types: 1) Good visions are glad tidings from Allah, 2) A terrifying vision caused by the devil, 3) Visions of a person’s thoughts.” 
It is only the first category of dreams that are meaningful. The rest are merely visions that revolve around what a man thinks during the day or are frightening dreams infused by Shay’tān in the subconscious mind of a person. Such dreams are meaningless.
As far as interpreting the dreams is concerned, there are no stipulated conditions for ascertaining the truth of a dream. Rather, there are a number of signs and factors that indicate towards a dream being true. However, the truth and falsehood of dreams cannot be decisively stated from merely looking at these signs and factors. It may happen such that despite the signs and factors being present, the interpretation of the dream may not materialise in real life.
Some of these signs are:
A number of people see the same dream.
The same dream is seen repeatedly by the same person.
The dreams seen in the later portion of the night.
Dreams seen in times closer to Qiyāmah, when men of knowledge will be scarce.
Dreams seen at such a time of the year when the length of the day and night are equal i.e. in spring and autumn (March and September). 
Dreams seen by a truthful person.
And Allah Ta’āla Knows Best
Student Darul Iftaa
Checked and Approved by,
Mufti Ebrahim Desai.