There are three levels of fasting, the general fast, the specific fast and the more specific fast.
As for the general fast, then it is the refraining of ones stomach and their private parts from fulfilling their desires.
The specific fast is the refraining of ones gaze, tongue, hands, feet, hearing and eyes, as well as the rest of his body parts from committing sinful acts.
As for the more specific fast, then it is the heart’s abstention from its yearning after the worldly affairs and the thoughts which distance one away from Allaah, as well as its (the heart’s) abstention.
From all the things that Allaah has placed on the same level. 
From the characteristics of the specific fast is that one lowers his gaze and safeguards his tongue from the repulsive speech that is forbidden, disliked, or which has no benefit, as well as controlling the rest of his body parts. . In a hadeeth by al-Bukhaaree: ‘‘Whosoever does not abandon false speech and the acting upon it, Allaah is not in need off his food and drink.’’ 
Another characteristic of the specific fast is that one does not overfill himself with food during the night. Instead, he eats in due measure, for indeed, the son of Aadam does not fill a vessel more evil than his stomach. If he were to eat his fill during the first part of the night, he would not make good use of himself for the remainder of the night. In the same way, if he eats to his fill for suhoor, he does make good use of himself until the afternoon. This is because excessive eating breads laziness and lethargy therefore, the objective of fasting disappears due to one’s excessiveness in eating, for what is indeed intended by the fast, is that one savours the taste of hunger and becomes an abandoner of desires.
 (Editors note: Additional comment is required here, The levels mentioned are levels of abstinence. The first of these three levels entails the abstinence which is fulfilled, the fast is considered complete in view of the one having met the legislated requirements [i.e. It does not have to be repeated or made up, the servant has indeed fasted.] The remaining levels deal with the value of the Fast. If the second is level is not met, the fast will be of less value to the servant, than if it were met and likewise for the third. Thus it is said that intentional eating and intercourse render the fast null and void, whereas committing other unlawful acts such, likes speaking falsely, placing the unlawful look to the opposite sex and so on will constitute a sin of one degree or another, but not nullify the fast.
 Related by al-Bukhaaree (4/99)
Posted from : The Inner Secrets of Fasting
Imam Muwaffaq-ud-Deen Ibn Qudamaah Al-Maqdisee
Read full article here @ http://abdurrahman.org/ramadhan/inner-secrets-fasting.html
Shaykh Ahmad ibn Ahmad Shamlaan (may Allaah preserve him) mentioned thirteen mannerisms that are to be observed for the one eating the Sahoor:
- Sincerity of the intentions
- Saying Bismillaah when one is about to eat, eating with the right hand and eating from that which is closer to you. Based upon the Hadeeth Umar ibn Abee Salamah.
- Gathering together upon the food. Indeed in that there’s a blessing.
- Not being wasteful in the meal and praising Allaah for it.
- The the meal is from lawful wealth. Indeed it is stronger for the (carrying out) the act of worship. Indeed Allaah is good and He only accepts that which is good.
- Having concern for the (proper) time (regarding the Suhoor)
- Seeking the forgiveness and making supplication in abundance during the time of as-Sahar (last part of the night shortly before the break of dawn). For indeed it is a blessed time (period).
- Give Sadaqah during that time and being diligent to be one who aids the one who has the ability to fulfill the fasting by feeding him the sahoor.
- Washing the mouth good along with the usage of the Siwaak. This is in order that the traces of the food do not remain in the mouth which will cause the one fasting doubt if it was to overwhelm him and enter down his throat.
- Waiting after the eating of the Sahoor for the purpose of performance of the dawn prayer. How praise worthy it is if the person was to go to the Masjid and wait for the prayer. Indeed that is stronger for him upon that (matter of praying the Fajr prayer on time). This is the case especially when many from amongst the people stay awake during the nights of Ramadaan up until the (time for) Sahoor. They eat the Sahoor then lay down. As a result of that, sleep overcomes and they miss the prayer. It’s possible that the person doesn’t get up until after the sun rise and some mid-day.
- Taking the food that is suitable for the condition of the one fasting. Like eating the dates along drinking milk and that which is similar to it.
- Getting the children accustomed to eating the Sahoor and fasting.
- Giving precedence (to others over oneself).
Taking from “Ad-Dururul-Manthoor fee Ahkaamil-Iftaar was-Suhoor” pg. 79-80 by Shaykh Ahmad ibn Ahmad Shamlaan (may Allaah preserve him)
Translated by Abu Yusuf Khaleefah USA NYC
8th day of Ramadaan 1433/ 27th of July 2012
Al-Imaam Muhammad ibn Saalih al-’Uthaymeen (may Allaah have mercy upon him) stated:
“In this matter there are five categories:
- The person is sure that Fajr hasn’t appeared. As an example: The appearance of Fajr is at five o’clock and the person ate and drank at four thirty. His fast is sound.
- The person is sure that Fajr has appeared. As an example the person ate at five thirty (although Fajr appeared at five). This person’s fast is invalid.
- The person eats but he’s not sure whether or not Fajr has appeared. However it overwhelms his belief that Fajr hasn’t appeared. His fast is sound.
- He eats and drinks and it overwhelms his belief that Fajr has appeared. His fast is not sound.
- He eats and drinks wavering back and forth (as to whether Fajr has appeared or not) and there’s nothing overwhelming with him in this matter. His fast is sound.”
The Shaykh went on to say:
“Even if it becomes clear to him that Fajr had appeared already, his fast is sound based upon (the principle in Islaam of) being excused due to ignorance in this situation.”
Taken from: “ad-Durur al-Manthoor fee Ahkaam al-Iftaar was-Suhoor” pg. 76 Quoting from Imaam al-’Uthaymeen’s explanation of Zaad al-Mustaqnaa (6/408-409)
Translated by Abu Yusuf Khaleefah Masjid Nur Allaah
2nd Night of Ramadaan/ 21st of July 2012