You ask how to use fasting with prayer

The direct benefits of fasting are that if you miss a meal, and use that time to pray and talk to the Lord about your needs, your nation's needs, and God's direction for your life, you will be blessed.

Some people fast one meal in a day, or one whole day each week, while others fast for a week or more when they have a burden the Lord has not lifted from them.

The key is to use the time to pray.

If you are lookng at a long-time fast, I would advise you to talk to your Spiritual Leaders, and learn how to enter and especially how to exit from a long fast. There are books available from Christian bookstores on this subject.

There is a good online series of articles you can see from this link on fasting by Dr. Bill Bright

(Link accessed 2015-03-20)