Praise be to Allaah.
Islam allows the man to look at his fiancée and speak to her about necessary matters to do with the marriage, and the man is encouraged to look at his fiancée when thinking of proposing, because that will bring their hearts closer together and generate the love and compassion that are the aim of the marriage.
It was narrated from al-Mugheerah ibn Shu’bah that he proposed marriage to a woman, and the Prophet (peace and blessings of Allaah be upon him) said: “Look at her, for that will help bring your hearts together.”
Narrated by al-Tirmidhi (1087); he said: this is a hasan hadeeth.
What it means is that it helps to create love and harmony between you, because if you marry her after having gotten to know her, in most cases there will be no regrets.
See: Tuhfat al-Ahwadhi.
There is no sin on you if you sit with your fiancée in order to work out some details of the wedding, but you should not be alone with her, so one of her mahrams or her mother should sit with you, and there is nothing wrong with that in sha Allaah.
Shaykh Ibn Baaz (may Allaah have mercy on him) was asked the following question in Majmoo’ al-Fataawa (20/429):
I love a girl very much and she also loves me. I have seen her only once, and I started to speak to her by phone within respectable limits, and we agreed to get married. Most of my conversations with her have to do with married life and the mutual understanding between spouses that is necessary, and how a wife should treat her husband and look after his house, and so on. Is it permissible for me to speak to her if she calls me, or is that not permissible?
He (may Allaah have mercy on him) replied:
If a man wants to propose marriage to a woman, it is permissible for him to speak with her and look at her without being alone. When a man came to the Prophet (peace and blessings of Allaah be upon him) to ask his opinion, he said: “Have you looked at her?” He said: No. He said: “Go and look at her.” And he said: “When one of you proposes marriage to a woman, if he can look at that which will encourage him to go ahead and marry her, let him do so.” Narrated by Abu Dawood (1783).
Looking is more serious than speaking, so if the conversation has to do with the marriage and where they will live, and how married life should be so that he will know whether she is familiar with these issues, there is nothing wrong with that if he wants to propose marriage to her. But if he does not want to propose marriage to her, then he has no right to do that. So long as he wants to marry her, it is permissible for him to talk to her about the engagement and about that which will encourage him to marry her, and she may do likewise, so long as they are not alone together; rather it should be done from a distance and in the presence of her father, brother or mother etc.
And Allaah knows best.