Before dealing with the subject in question, it has to be noted that unlike  the common perception which restricts sustenance to its material manifestations, the term rizq (sustenance) has a wide ranger of meanings that include all divine bounties irrespective of the bounties being material or spiritual. Thus, health, tranquility, success over doing obligatory duties such as performing hajj, having a good friend etc. are all considered to be examples of sustenance.  Indeed, there are some traditions which also refer exclusively to material sustenance which will be mentioned as follows:
1. Struggle for acquiring sustenance: Imam Sadiq (AS) says in this regard:  "One who goes in search of little sustenance will ultimately gain abundant rizq and he who does not go in search of little sustenance, will end up losing the abundant sustenance too."[1]
2. Prayer and supplication for an increase in sustenance: There is a specific title in the book of Al-Kafi about an increase in sustenance.[2] In this chapter of the book, certain supplications have been recommended for increase of sustenance. For example, there it has been narrated that Imam Baqir (AS) said to Zaid Shahham: Read this dua in the sajdahs of your prayers for an increase in your sustenance:
"يَا خَيْرَ الْمَسْئُولِينَ وَ يَا خَيْرَ الْمُعْطِينَ ارْزُقْنِي وَ ارْزُقْ عِيَالِي مِنْ فَضْلِكَ الْوَاسِعِ فَإِنَّكَ ذُو الْفَضْلِ الْعَظِيم"[3]
Transliteration: Yaa Khairal Mas-ooleen wa Yaa Khairal mo’-t’eenar zuqni war zuq ayaali min faz”likal waasi’. Fa innaka dhul faz”lil A’z’eem.
"O the Refuge of those ask for help, O the berst of the bestowers, bestow upon me and my family your abundant rizq because you are the possessor of extensive grace."[4]
A man from the companions of the Prophet (S) had long not visited His Holiness. Upon seeing the Prophet (S), His Holiness asked him, "What made you  not to visit us."
He said that he could not come due to illness, poverty and need.  The Prophet (S) then said: "Don't you want me to teach you a dua which will rid you of illness and poverty?"
"O Messenger of Allah" he said "may Allah's blessing and mercy be upon you, teach me that dua."  Then the Prophet (S) told him to recite:
لَا حَوْلَ وَ لَا قُوَّةَ إِلَّا بِاللَّهِ الْعَلِيِّ الْعَظِيمِ تَوَكَّلْتُ عَلَى الْحَيِّ الَّذِي لَا يَمُوتُ وَ الْحَمْدُ لِلَّهِ الَّذِي لَمْ يَتَّخِذْ صَاحِبَةً وَ لَا وَلَداً وَ لَمْ يَكُنْ لَهُ شَرِيكٌ فِي الْمُلْكِ وَ لَمْ يَكُنْ لَهُ وَلِيُّ مِنْ الذُّلِّ وَ كَبِّرْهُ تَكْبِيرا[5]
"La haw la wa la quwata illa billahil 'aliyil azim tawakkaltu ‘alal hayyil lazi la yamutu wal hamdu lillahil lazi lam yattahkhiz saahibataw wala laa walada wa lam yakun lahu sharikun fil mulk wa lam yakun lahu waliyun minaz zulli wa kabbirhu takbira."
As reported, it did not take long until one day the same man returned and said to the Prophet (S): "God ridded me of illness and poverty (by means of that dua)."
3. Staying awake between dawn and sunrise:  Muhammad bin Muslim asked Imam Baqir or Imam Sadiq (AS) about sleeping after Dawn Prayers to which the Imam replied: "Sustenance is distributed at this time and I do not like anyone to be asleep at this moment."
As well, Imam Sadiq (AS) said: "Morning sleep is bad and it makes man's one face look yellow and ugly. Such a sleep is the sleep of  people who are deprived of (divine blessings), and God distributes the sustence of His servants from dawn till sunrise."[6]
Offering night prayer:  It has been reported from Imam Sadiq (As) that a man was complaining about indigence and extreme poverty so much that he was even about to complain about his hunger. Addressing him, the Imam said: "O man, do you ever offer night prayer (salat al-layl)?"
"Yes" he answered. 
Facing his companions, the Imam (AS) said: "One who claims to offer night prayers but he remains hungry during the day is not but a liar. Verily, God, the Almighty and Glorified, has promised to give, during the day, rizq (sustenance) of the individual who estalishes night prayer."[7]
The deeds which cause sutenance to increase are  too many and we suffice to this much.  Now we shall mention in brief some  of the factors which are responsible for a decrease in the amount of rizq (sustenance):
1. Intention (niyyat): There is no doubt that intention has an impact on the individual's sustenance causing his sustenance to either increase or decrease depending on the nature of his intention. Imam Ali (AS) says: "Man's sustenance is to the extent of his niyyat"[8] This saying of th Imam (AS) suggests that man's intention impacts one's sustenance and it makes it either decrease or increase. Hence, if a person intends to help provide his family with food and other means of livelihood, God shall increase his sustenance and if he intends to put them into hardship and distress, God too shall put him into hardship and distress.
2. There are some habits which have been introduced as factors responsible for reduction of sustenance.  It has been reported from the Comamnder of the Faithful, Ali (AS) that he said: "Not wiping off the spider web in one's house, answering the call of nature in a bathroom, eating and drinking in the state of janabat, brushing the teeth with tamarisk, combing the hair while standing, keeping garbage at home, making a false oath, adultery, sleeping between Maghrib and Isha, sleeping before sunrise, the habit of lying, listening to frivolous songs too much, turning away a needy person at night, not observing moderation in the expenditures, and cutting off ties with relatives are among the causes of reduction of sustenance…[9]
The Messenger of Allah (S) said: There are twenty habits which lead to a decrease of the sustenance including getting up from bed to urinate while naked, not washing hands before eating, demeaning even a small morsel of bread, burning onion and garlic peelings, sitting on doorsteps, sweeping house at night or sweeping it using a dress/clothes, cleaning the house with an end of one's clothe, wiping limbs with hems or sleeves, leaving dirty dishes/utensils at night, leaving drinking utensil uncovered, making haste to exit the mosque, going early to the mall (market) and not coming back from the mall till late, buying bread from the poor, cursing one's children, sewing clothes while they are worn and putting out a lamp by blowing on it.[10]
For further information refer to question 3783 (site: 4007) Index: Sustenance is decreed, and question 2626 site: 4801 index: Dua for acquiring wealth.
 

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