It is something that you will learn and become better at as you share your married life together. Becoming one means loving each other, sharing your lives with each other, taking each other into consideration always. Becoming one means getting rid of all selfishness out of your lives because there is no room for selfishness in marriage. If selfishness is not rooted out or creeps in later on, its sure to cause problems. If God blesses your marriage with children, then you will also take your children into consideration in all that you do.
Marriage is a school of love.
You will probably discover weaknesses in the other which you do not now know. This will be an opportunity to love the other, heal the other, forgive the other. There will be times when like at the wedding at Cana it will seem as if the wine really has run out, times when you will forgive each other and make a fresh start. Marriage is also a school of forgiveness. What I have spoken about up to now is the human aspect of marriage.