Fasting is fastening or afflicting your body in order to edify your spirit. Fasting is neither an advice nor an admonition. Fasting is a commandment (Mat.6:17)
Isaiah 58:5-6 KJV
“Is it such a fast that I have chosen? a day for a man to afflict his soul? is it to bow down his head as a bulrush, and to spread sackcloth and ashes under him ? wilt thou call this a fast, and an acceptable day to the Lord ?  Is not this the fast that I have chosen? to loose the bands of wickedness, to undo the heavy burdens, and to let the oppressed go free, and that ye break every yoke?”
There is a chosen fast and an inspired fast. A chosen fast is a proclaimed. Example of an inspired fast is the fast embarked upon by Ezekiah. Do you want a change of situation? Be inspired to fast.
Matthew 6:6, 17 KJV
“But thou, when thou prayest, enter into thy closet, and when thou hast shut thy door, pray to thy Father which is in secret; and thy Father which seeth in secret shall reward thee openly.  But thou, when thou fastest, anoint thine head, and wash thy face;”
The word “when” connotes time. That means there is a particular time that you must fast….Prayer is the value offer in the fast. Prayer is what gives value to our fasting. Fasting without prayer is a wasteful exercise. It’s a mere punishment.
Mark 9:29 KJV
“And he said unto them, This kind can come forth by nothing, but by prayer and fasting.”
What are the profitable approaches to fasting and prayer?
1). Come into fasting and prayer with praises – If you’re not joyful you will be fretful. Don’t come into fasting and prayer with murmurings.
Philippians 2:14 KJV
“Do all things without murmurings and disputings:”
2). Enter into fasting and prayer with expectations – It’s so disgusting to see many believers who come to God without an expectation. Be expectant. Without expectation there will be no manifestation.
Proverbs 23:18 KJV
“For surely there is an end; and thine expectation shall not be cut off.”
Also, be specific with your expectation(s). God does not take assumption, be specific in your demand(s). For instance, if you’re looking for a child, what type of child do you want? Male or female.
Mark 10:51 KJV
“And Jesus answered and said unto him, What wilt thou that I should do unto thee? The blind man said unto him, Lord, that I might receive my sight.”
3). Come with prayer – Make sure that you pray. God does not answer fasting. Prayer is what God answers. Fasting is meant to facilitates answered prayer(s).
Matthew 17:20-21 KJV
“And Jesus said unto them, Because of your unbelief: for verily I say unto you, If ye have faith as a grain of mustard seed, ye shall say unto this mountain, Remove hence to yonder place; and it shall remove; and nothing shall be impossible unto you.  Howbeit this kind goeth not out but by prayer and fasting.”
In the above scripture, Mountain can only be moved by “fasting & prayer” – not fasting alone. Listen: There are certain mountains that will not give way until you fast.
4). Come with thanksgiving – Prayer(s) unaccompanied with thanksgiving may not fulfill its potency. Thanksgiving is the seal of answered prayer.
Philippians 4:6 KJV
“Be careful for nothing; but in every thing by prayer and supplication with thanksgiving let your requests be made known unto God.”
In English language, the word “with” plays the role of emphasis (importance). Hence, ensure that you wrapped up your prayer with thanksgiving.
The following are the blessings & benefits of fasting and prayer
Authority, Wonders, Miracle, Breakthrough, Revelation, insights, Restoration, Illumination, Divine ideas, Overflowing blessings, Healings, Divine Health, Moved Mountains, barriers, & obstacles, Dispelled Darkness, Emits Light, Multipurpose Solution, Turn around, Strength, Longevity, Dominion, Wealth, exploits, New heights, Ground breaking & explosive testimonies, Destroyed yoke, Freedom from Satanic oppression, breaking of negative habits, Sanctification, Liberation & speed, access to deep-things (divine secret)
References: Is.58:5-14, Is.40:31, Mat.17:21, PS.25:14
Your questions are mostly welcomed.