The advice that is most commonly given is to first of all have love and do not judge. With love, pray for the one who is not now interested in spiritual matters.
Here is advice from Elder Paisios when asked about this by a woman concerned about her husband:
Entrust him to Christ and pray that his heart be softened. Eventually little by little, Christ will descend in his heart, and he will start speculating. As soon as his heart is somewhat softened, then she can ask him, for example, to drive her to church. She shouldn't say to him, "Come to church with me," but "Can you please take me as far as the church?" If he takes her all the way to the church, then he might say to himself, "I've come this far; why don't I go inside and light a candle?" In this way, little by little, he may make progress.With prayer and kindness coupled with patience you can lead your spouse to open their heart to a more spiritual way of living. If you do not approach this with love and tenderness then their heart will be hardened and your relationship potentially damaged. By seeking to discover the little nudges you can provide you can lead your spouse in the right direction. But you have be clever so that your nudges do not become nagging.
Your spiritual father can also be of help. He can help you develop your own spiritual life so that your goodness will be transferred to your spouse.
Elder Paisios points out that women tend to be pious by nature. But once a man becomes interested in his spirituality, not even his wife can keep up with him. Then the wife must be careful not to become envious of his progress. If she begins to complain about all his spiritual endeavors and calls him a monk or priest in protest, then the man needs to tread very carefully. The aim is to grow together, but you will not always be on the same step.
If a difficulty arises in this case here is what advice Elder Paisios gives to the husband,
To keep the family from falling apart I advise the husbands, "When the right moment comes, tell your wife: 'If I go to church and pray a little and do some prostrations, or if I read a spiritual book, I'm not doing this out of an abundance of devotion, but only as a means of self-restraint, to keep me from being led astray by our wretched society and getting involved with bad company.'" If the husband handles it carefully then the wife will be happy and may even go on to outdo her husband spiritually. But if he is careless and insensitive, he'll crush her...For many years in my own life it was my wife who was interested in spiritual matters and insisted on going to Church regularly. I would find excuses to not go. But, thank God, she was patient and prayed for me. Eventually Christ got hold of me and I could not get enough. I read everything, I went to church regularly, I prayed daily, I sought counsel from a spiritual father frequently. Then I became worried that my wife was not showing the same interest as I now felt. Somehow God gave me the insight to understand that we must walk this path together and that we would not always be on the same step along this long path. So instead of going my own way, I sought ways to involve her in my efforts and was careful not to judge, but to appreciate how she led me to what now gave me great inner joy. Through God's guidance we have continued to walk a path together. We pray together, we go to services together, we share what we are reading. We have found that an active spiritual life nurtures our love for each other. We still have our arguments but they do not last long.
The challenge for all couples is to seek a shared path realizing that this may take many years to achieve but with sincerity on the part of either one of the couple, the other will be brought along with them and may eventually surpass them. It then becomes a beautiful dance where each leads the other at different times. This is the way we have been able to grow old together.