Praise be to Allah.
Looking at the woman to whom one wants to propose marriage has only been made permissible because of necessity, to be certain and put one’s mind at rest, and in order to follow the Sunnah, as mentioned in the hadeeth of al-Mugheerah and others. But four necessary conditions apply:
The first is that one should be serious about marriage; the second is that the man and woman should not be alone; the third is that there should be no fear of fitnah (temptation); and the fourth is that it should not go beyond the limits set by sharee’ah, i.e., looking at what usually appears, which is what she shows to her father, brother and other mahrams. See Question #2572. On this basis, a man should not look at any woman except the one whom he seriously wants to marry. If he is pleased with her, (he should proceed with marriage), otherwise he should move on to another. And Allaah knows best.