If we take any rituals of Islam, we can find out that it related with some rules and regulations, such as its Sharths (conditions), Fards (integrals), Sunnaths (desirable), Mubthilaths (Nullifiers) and so on. Hence, the fasting has also suchlike things as follows:

Integrals of fasting

In fact, the fasting has two integrals (fards): 1. the intention (Niyya’th) i.e. each night to make the intention to fast the following day 2. To abstain from all things those make the fasting in futile such as the sexual intercourse, masturbation, and inserting anything with a volume into the head or the body cavity through an open inlet, excluding one’s pure saliva while still inside the mouth, during the time from the dawn until the sunset.

 The intention (Niyya’th)

Its intention is to bear the fasting in mind but it isn’t necessary to chant it. But it is important to put each intention for each fasting. Its shortened form: “Navaithu sawma ramadana” I bore the fasting of Ramadan in the mind. Its full form: Navaithu sawma ghadhin a’n adhai’ fardi ramadani hadihi ssanathi lillahi tha’ala (I bore in mind to perform the fasting of this year tomorrow for the sake of the God Almighty as in its fixed time (ada’). One should make the intention at night to fast the following day. It means that to have the intention to fast in one’s heart during the night preceding the fasting day i.e. after the sunset and before the dawn of the following day. As related by at-Thurmudhi, an-Nasa’i, and others, the Prophet (Pease and Blessing of Almighty be upon him) said: “The intention is in the heart and does not have to be uttered with the tongue. If one slept at night without making the intention to fast and woke up after the dawn, then he is obligated to abstain from whatever a fasting person would abstain. Afterwards, he should fast a make up for that day. In the matter of woman, if her menstrual or postpartum bleeding stopped at night, then she must intend to fast the following day. The purifying bath is not required to start fasting, but rather to start praying.

The time of having intention

The intention for any obligatory fasting, must take place at the night before the fast. However, it is not conditioned upon one who is performing an optional fast. Because, It is valid for him to make the intention that same day during the morning, before the sun moves from the center of the sky towards the west, as long as he had not committed any of the invalidators of fasting since the dawn appeared.

Nullifiers of fasting (Mubthilaths)

The fasting person must abstain from all sorts of invalidities of fasting. He must abstain from taking into his body cavity any material like food or drink or other than that which has a tangible volume from an open inlet such as the mouth, nose, anus, vagina and other. If a person deliberately did so, while remembering he is fasting and knowing that it is unlawful to do so and not because one threatened him to kill (or the like) if he did not break his fast, then this invalidates his fast; besides he has to make it up. Materials which are absorbed by the pores of the skin do not invalidate the fast, because it is not an open inlet to the body cavity. For instance, rubbing oil into the skin does not invalidate the fast.

If some saliva was spit outside the mouth separating from the tongue, even to the lips, then was taken back in and swallowed, it would invalidate the fast. However, if the saliva is mixed with something else and then swallowed, it also invalidates the fasting. So, someone whose gums bleed must obligatorily wash his mouth thoroughly with water.  Spitting is not sufficient.

If one rinses the mouth during ablution [wudu] without exaggeration and some water reaches the body cavity, one’s fast is not nullified.  But if one rinses the mouth for other than the ablution (such as to cool off or for cleanliness) and water reaches the body cavity, one’s fast is nullified even if one did not exaggerate.  Similarly, one rinses the mouth during ablution and exaggerates in doing so (by gargling, for example); then one’s fast will be nullified if any water reaches the body cavity.

If one performs an obligatory purifying bath [ghusl] (such as for major ritual impurity or menstruation) or a recommended one (such as for the Friday prayer) and water reaches the inside of the ears, one’s fast is not nullified (if it is without exaggeration and without diving in river). One’s fast is not broken, if it is too hard to protect himself from swallowing, like the dust of the street or the flour and the like.

Like wise, It is permissible (although disliked) to taste food with the edge of one's tongue, provided nothing reaches the body cavity.  The cigarette smoking breaks the fast of the smoker himself, but not breaks the fast of the person nearer to him who breathes in some of that smoke. Nose-drops nullify the fast. An anal suppository will nullify the fast so, if one is able to delay it until after sunset, it is obligatory to do so.  If one needs it during the day, however, and is unable to delay it, one may take it and it is obligatory to perform a make up fast instead of that day. Entering a stick in order to clean the inside of the ear nullifies the fast. The inhaler used by asthma patients nullifies the fast because particles like drops of water come out of it and mix with his saliva, after which the patient swallows it, causing him to break his fast.

Likewise, he must abstain from sexual intercourse during the day of fasting. If he did not know the abstaining from sexual intercourse during the fasting or he forgot that he was fasting and he performed this act, then it does not invalidate his fast. However, if one, whether it is man or woman, does sexual intercourse during the fasting while knowing this is unlawful and remembering he is fasting, then it would invalidate his/her fasting. More over, they should pay the expiation (Kaffara) for invalidating their fasting by sexual intercourse. Their expiation is in the following order: 1) to set a Muslim slave free. 2)  If he was unable (like India in which the slaves are unavailable), then to fast two consecutive months, other than making up the day which was invalidated by his sexual intercourse. 3) If unable (by sick or old age), then to feed each one of 60 poor people two cupped average-sized handfuls of the most common staple food of the country.

One’s fasting is broken by masturbation or making the semen come out of one using his own hand or the hand of his wife or because of a kiss or because of other physical contacts. In other hand, if a person experienced a wet dream or semen exited from him because of certain thoughts, then it wouldn’t invalidate his fasting.
To vomit deliberately invalidates the fasting by inserting one’s finger into his mouth or by other methods. Besides, he has to make it up. However, the one, who vomited unintentionally, does not break his fast as long as he does not swallow any of the vomit or saliva mixed with the filth (Najas).