Fasting is abstaining from food or some other desire for spiritual purposes. We humbly deny something of the flesh to glorify God, focus our spirit, and go deeper into our prayer life.
The purpose of fasting is to move our minds away from this world and devote our thoughts to God. Fasting is not intended to be a punishment for the flesh but to focus on God. There are several reasons Scripture gives to fast: repentance; spiritual strength against an enemy attack; to test what desires control us; and to divide our food among the poor. Scripture also warns us not to fast to be seen by others or to be commended by God. It is wise to examine your motivations when considering a fast.
Generally speaking, when Scripture addresses fasting, it has to do with abstaining from food. This can be a partial fast, as in giving up certain types of food or certain meals (Daniel 10:2-3), or a complete fast, where only water is consumed (Luke 4:1-2). That being said, anything you can temporarily give up in order to focus on God can be considered a fast (1 Corinthians 7:2-5).
As a final note, please consider your own health when fasting. If you are diabetic, pregnant, breastfeeding or have a history with an eating disorder, it's not a good idea to fast from food. Your health is important, and there is absolutely no shame in choosing not to fast from food. It may be helpful to fast from something else instead of food. You know your body and history best and can make the best decision for your own spiritual and physical health.
Decide what to temporarily give up to focus on God. This can be food, specific meals, television, social media, or just about anything to focus on God. If you decide on food, decide if this will be a partial or a full fast (no food, only water).
The point of fasting is to focus on God, so decide what you will use to replace whatever you're fasting from. This can be more prayer time, time sharing the gospel, time serving the poor, or other God-focused activities.
Decide how many days and for how long each day you will fast. You may want to consult a physician if you plan to fast from food for longer than a couple of days.
In the week or so leading up to your fast, you may wish to cut back on whatever you are fasting from gradually. Cut back on caffeine intake if you are planning on fasting from caffeine. If you are new to fasting, it is wise to build up to longer fasts; start with skipping one meal and work your way up from there.
The first few days of the fast will likely be the most difficult. Ask God to give you strength to push through the difficulty of the fast, and focus on him during this time. Be attentive to what God is saying to you during this time.
Pay attention to what your body and spirit are telling you about the fast. When you are breaking an extended food fast, be careful not to end abruptly. Start by taking in small amounts of food and juice, and work your way back up to your normal diet.