Our elders follow the practice of chanting Ashtaksharam immediately after performing sandhyavandhanam. As Swami Desikan has shown this in Sri Pancharathra Agama Raksha based on authoritative statements from Mahabharata, our elders follow this practice. Chanting Ashtaksharam at this time cleanses the soul to worship Him.
Generally, only those who have undergone Samashrayanam are allowed to chant. One has to chant the thaniyan (invocatory verse) of the Samashrayana Acharyan and the lineage of Acharya and then one has to recite the sloka ‘Asmad Desikam Asmadiya Pracharyan’ and ‘enuyir thandalithavanai’ sloka as per the tradition.
To know about how to do pranayamam, sankalpam and about the Mahabharata verse please click the following YouTube link