What are the conditions that render acts of worship valid?

All perfect praise be to Allaah, the Lord of the worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad, sallallaahu ‘alayhi wa sallam, is His Slave and Messenger.

There are two types of conditions that must be fulfilled for acts of worship to be valid. First, the general conditions that are obligatory for all acts done for the sake of Allaah The Almighty. These can be summarized as: belief in Allaah The Almighty, and sincerity in dedicating the deed to Him; Allaah The Almighty Says (what means): {Unquestionably, for Allaah is the pure religion.}[Quran 39: 3] 

A necessary general condition is that acts of worship must be done in accordance with the teachings of  the Prophet, sallallaahu ‘alayhi wa sallam, as he, sallallaahu ‘alayhi wa sallam, said that any act of worship that varies from  his teachings and example is rejected. [Al-Bukhari and Muslim]

Each act of worship has its own necessary prerequisites for it to be considered valid, such as the conditions for performing prayer, observing fast and performing pilgrimage. 

Furthermore, some daily life activities have certain conditions that must be fulfilled in order for them to be considered as permissible. An example of this is the conditions for making financial transactions permissible. In the books of Fiqh (Islamic jurisprudence), these conditions are mentioned in the appropriate section. 

And Allaah Knows best.