Puranas mention that Thiruvonam is the thirunakshtram of Emperuman. Sravana Vratam is associated with Him.
As the vratam is observed for Emperuman, all our good activities are fructified due to His grace. Hence it is considered special.
How to observe the Vratam?
One should observe Vratam after purification and recite Daya Satakam, and other Keertanas.
One must avoid indulging in leisure activities and entertainment.
This is observed for the Lord Thiruvenkatamudayan and Oppiliappan. If it is observed for Lord Oppiliappan food must be cooked without salt.
One should partake in food only once and if required one can take palahaaram (light refreshments) in the evening.
It is not a must to observe this Vratam like Ekadasi Vratam.