Some of the mistakes that fasting people make in regard to Suhoor are:

1-Some people do not have Suhoor and this is contrary to the Sunnah. It is from the guidance of the Prophet to have Suhoor if the person intends to observe obligatory or voluntary fasting. Urging Muslims to have Suhoor., he said:

• “Have Suhoor, as indeed there is a blessing in it.” [Al-Bukhari and Muslim]
• “The difference between our fasting and the fasting of the People of the Book is the (meal of) Suhoor.” [Muslim]

2- Having Suhoor early in the middle of the night or one or two hours before dawn is also contrary to the Sunnah. The Prophet said: “Hasten to (eating) Iftaar (in Ramadan immediately when the time is due), and delay (eating) Suhoor.” [At-Tabaraani] It is an act of the Sunnah to have Suhoor just before dawn (approximately half an hour before it). Anas he said: “The Prophet and Zayd ibn Thaabit, may Allah be pleased with him, had Suhoor. When they finished, the Prophet left for the prayer. Anas, may Allah be pleased with him, was asked how much time was there between their finishing Suhoor and entering the prayer; he said: ‘Enough time for the recitation of fifty verses (of the Quran).’” [Al-Bukhari]