First day fasting is the hardest thing. I couldn't understand why we get this massive headache.
I found this article about Fasting Tips.
Consider Your Schedule
While a fast, by nature, is inconvenient, it should be an inconvenience to you—not to those around you. You should not obligate your family to skip Christmas dinner because of your fast. This takes away the personal nature of fasting.
Tell Only the People You Must
Your spouse will need to know you are fasting. Beyond that, you would be better off not telling many people that you are fasting. Most won’t understand. Fasting can also become a source of pride and boasting as you spread the news to more and more people.
Telling your pastor can be a help both to you and to him. It will be an encouragement for him to pray more specifically for you during this time. And you will know that someone is praying for your spiritual and physical well being.
Wean Yourself Off Caffeine
Several days before your fast begins, you should start weaning yourself off caffeine. Some people experience unbearable headaches 2 to 3 days after ceasing to drink caffeinated products. During your fast you will already be acutely aware of your stomach. There is no need to add a second discomfort if it can be avoided.
Disconnecting from TV, radio, newspapers and the Internet can help you stay focused on your purpose for fasting. You will be less tempted by the constant bombardment of advertising as you become physically and emotionally challenged. Avoiding media will give you more time to focus on the Lord and His Word.
Disconnect from people
Fasting is not necessarily a vacation, though dedicating time off and away from people during your fast can help you get the most benefit out of this precious time. Leave your email and cellphone behind. If possible, find someone who can cover your responsibilities at work and ministry. Many people fast and still carry on their normal daily activities. But if you can get away, it will give you more time in quietness and stillness with the lord.
Beware of Your Emotions
Some people experience vast mood swings during a fast. One moment they are totally focused on God and the next they are wallowing in pity. Knowing that this is likely to happen will help you react properly. Learning to refocus on God and His goodness during this tough emotional time will help when your fast is over and you experience similar emotions.
Laziness is a problem that the Bible speaks against, but most of us today suffer from being too busy and not getting the rest we need. If you disconnect from the media and other people you will have extra time allowing you to get a full night’s sleep. During your fast you will be forced to slow down since you won’t be needing long meal breaks. A fast will reveal to you that you have too many activities and busyness in your day-to-day routine.
Stay Physically Active
You should take time to rest but this does not mean you should do nothing. Enjoy a walk in God’s creation. Outside of His Word, His creation is one of the best ways that God has revealed Himself to us.
Be Still and Focus on God
Fasting is a time to study God’s Word, meditate and pray. To help with this, plan a specific Bible passage or topic you want to study during your fast. Look for verses you want to memorize and meditate upon. Fasting by Jesus and the disciples was always accompanied by prayer. Spend time talking to God and allowing Him to reveal Himself to you in His Word.