It is always preferred to visit first Sri Padmavathi Ammavari Temple at Tiruchanur (lower Tirupati).
If one visits Sri Padmavathi Temple, before 9 am it will not be that much crowded and one can have peaceful Darsan of Sri Padmavathi Ammavari (Alamelu Mangai Thayar). If one visits by 4 PM, through by buying special ticket (before 4: 30 PM), Kunguma Archana can be performed; 2 persons per ticket are allowed during this time which is around 5PM. One may have very comfortable and peaceful Darsan during this Kumkum Archana. It is widely believed that one should preferably have darsan of Padmavathi Ammavari before having Darsan Of Lord Balaji at Tirumala. and it is also believed that Sri Ammavari recommends the devotee to Balaji to fulfill his/her prayers/requests.
In Vishnu Temples, normally one should not worship first Lord Vishnu’s idol before worshipping the Thayar ( Devi) and therefore after worshipping Devi (Lakshmi) only you should worship Perumal). This is applicable to Tirupathi also. However in Shivji Temples one should not worship the Amman (Ambal) before worshipping Lord Shiva. You should first worship Shivji and then worship Ambal.
It is also believed that Sri Varaha Swamy Perumal is the owner of the seven hills before Sri Venketeswara Perumal acquired to reside. So the practice is, every devotees FIRST visits Sri Varaha Swamy Perumal Shrine before vsisitng the main shrine Sri Venkateswara temple, since TIRUMALA belongs to Sri Varaha Swamy. The Temple is dedicated to Lord Varaha, and is situated on the northern premises of Sri Venkateswara Temple, Tirumala on north west corner of Swami Pushkarini. This temple is believed to be older than Sri Venkateswara Shrine. According to the Brahma Purana, pilgrims should first offer naivedyam to Sri Adi Varaha Swami, before visiting the Sri Venkateswara Temple.
According to Atri Samhita (Samurtarchanadhikara), the Varaha avatara is worshipped in three forms:
The idol of Sri Varahaswami in Tirumala is that of Adi Varaha, as it resembles the description of the Adi Varaha murti in Vaikhanasa Agama texts and therefore only by visiting Sri Varahasamy Temple, the Tirumala pilgrimage is complete.
As Tirumala temple is always crowded, one has to plan the visit suitably in advance. Padmavathi Ammavari temple visit should not be missed at any cost. if it is difficult to visit before Balaji Darsan one should make it a point to visit atleast after Balaji Darshan though visiting prior to Sri Balaji Dharshan is preferred.
Hope it is clear.