I have fasted on many occasions throughout the years; however, the length of time I fasted was generally the same: three days. I did so to get alone with God and to spend some seriously devoted time through prayer and the Word with the Lord.
If you are planning to pray at any time, you should always do so playfully. No jokes on this point. The enemy is watching.
I recall being on a fast once and having just started reading my Bible after spending time with God through prayer when close to five or six noisy and unavoidable distractions took place. I dealt with them with grace and patience, as I was aware that the enemy was at work to attempt to cause me to say or respond in a fashion that was not Christlike in any way. I dealt with them and continued spending time with God. The next day my neighbor came to me and began chatting with me and before they left, they offered me a big bowl of food that they had made and was leftovers from a family celebration that he had attended. I not wanting to offend him, took the bowl and placed the food in my fridge. I went to the Lord in prayer and began thanking the Lord out loud that while I was fasting the enemy was trying to offer me food to cause me to break my fast. I praised God for giving me insight as to what was going on and thanked Him for the strength to NOT eat the food until I had finished my fast.
Be mindful that the enemy will do ANYTHING to knock you off your path at any time. Specifically, even if it is one degree. Then accuse you and deride you for not having the strength and fortitude to follow through with the fast. I tell you, stay the course. PRAY, PRAY, PRAY!!!! Make a clear plan yet all the while being open to being guided by the Holy Spirit if God guides you in a specific direction both in prayer and in reading the Word.
During a fast, tell no one. I mean NO ONE!!! Why? First, in the Bible it tells you to not reveal this to anyone, and to speak with the Lord about it and not to man. Also, because it is not their business. You can ask for individuals or a group of Christian brothers and sisters to keep you in prayer and simply ask them to pray that God gives you focus and strength in the coming days and weeks. Keeping it in a general request also keeps prying minds away from asking for specifics. If they ask for specifics, tell them to just pray for you and that God is aware of what you need. Never tell others you are fasting. There are some brothers and sisters who are not at a mature level to keep what you tell them to themselves.
When you begin your fast, stay the course, the enemy will try you and attempt to keep you from following through on your fast. PRAY, PRAY, PRAY!!!!!
During a fast never reveal you are fasting, after you have fasted, discussing it here for the purposes of growth among the body of Christ is okay.