All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah, and that Muhammad is His slave and Messenger.
It is a Sunnah for a person who intends to ask for a girl's hand or to do an important action, to ask Allah (The Exalted) for proper guidance.
Jaabir Ibn ‘Abdullah narrated: “The Prophet would teach us (Muslims) the Istikhaarah (seeking Allah's proper guidance in something) prayer for all of our affairs as he would teach us a Surah from the Quran. He, (The Prophet ) said: 'If one of you is deliberating over an act, he should pray two supererogatory Rak’ahs and say: 'O Allah! I consult You as You are All-Knowing and I appeal to You to give me power as You are Omnipotent – I ask You for Your great favor, for You have power and I do not, and You know all of the hidden matters. O Allah! If You know that this matter (he should mention it) is good for me in religion, my livelihood, and for my life in the Hereafter, (or he said: 'for my present and future life') then make it easy for me and bless it. And if You know that this matter is not good for me in my religion, my livelihood and my life in the Hereafter, (or he said: 'for my present and future life') then keep it away from me and take me away from it and choose what is good for me wherever it is and please me with it.”
Then, i.e. after the Istikhaarah and consultation with your relatives and brothers in Islam, you may ask for the girl's hand from her guardians.
It is also a Sunnah to look at the girl you want to propose for the Prophetic Hadeeth that reads: “When one of you proposes to a woman in marriage, if he is able to look at what will induce him to marry her, he should do so.” [Abu Daawood and Ahmad]
After that, one has to cling to Islam and to provide himself with piety, patience, good treatment and good character.
At last, we remind you again that adherence to the above-stated points as described in the Sunnah will bless your family life and make you happy, Allah willing.
For more benefit on how to perform Istikhaarah and how to supplicate to Allah, please refer to Fataawa 172573, 81434, and 82964.
Allah knows best.