Richard Foster’s book “Celebration of Discipline” is a timeless classic has helped millions to discover a richer spiritual life infused with joy, peace and a deeper understanding of God.
It is still in print after over thirty years [Amazon] and highly recommended.
About fasting, Foster advice is:
In the beginning you will be fascinated with the physical aspects, but the most important thing to monitor is the inner attitude of worship. Outwardly you will be performing the regular duties of your day, but inwardly you will be in prayer and adoration, song and worship. In a new way, cause every task of the day to be a sacred ministry to the Lord. However mundane your duties, they are for you a sacrament. Cultivate a "gentle receptiveness to divine breathings."
Break your fast with a light meal of fresh fruits and vegetables and a good deal of inner rejoicing.
Drink only water but use healthy amounts of it. Many feel distilled water is best. If the taste of the water bothers you, add one teaspoon of lemon juice. You will probably feel some hunger pains or discomfort before the time is up. That is not real hunger; your stomach has been trained through years of conditioning to give signals of hunger at certain hours. In many ways your stomach is like a spoiled child, and spoiled children do not need indulgence, they need discipline.
Ignore the signals or even tell your "spoiled child" to calm down and in a brief time the hunger pains will pass. If not, sip another glass of water and the stomach will be satisfied. You are to be the master of your stomach, not its slave. If family obligations permit it, devote the time you would normally eat to meditation and prayer.
It should go without saying that you should follow Jesus’ counsel to refrain from calling attention to what you are doing. The only ones who should know you are fasting are those who have to know. If you call attention to your fasting, people will be impressed and, as Jesus said, that will be your reward. You, however, are fasting for far greater and deeper rewards.