What did Vishnu decide, listening to Gods?

इत्यतद्वचनम् श्रुत्वा सुराणां विष्णुरात्मवान्
पितरं रोचयामास तदा दशरथं नृपम्  

ityatadvacanam SrutvA surANAM viShNurAtmavAn

pitaraM rOcayAmAsa tadA daSarathaM nRupam

Shloka Translation:

Listening to the great words of the Gods, the great soul Vishnu
Decided that he will consider King Dasharatha as his father

Lord Vishnu decides on where he is to be born and who upon the request of the Gods, he had to choose as his father (Dasharatha). This shloka is available in the 15th Sarga of Balakanda within Maharshi Valmiki's Ramayana. Vishnu is the Lord himself who decides to be born after listening to the Gods about Ravana, who is in the world with his bad ruling and not being killed by anyone and since Dasharatha (who is a learned and a great king) was conducting a Yagna in anticipation of a Son, they all request him to provide a boon by dividing his divine soul into four and appear as four sons to Dasharatha's three wives. The next would be as to in what form Vishnu assures and blesses the Gods that he would fulfill their request.