The Means and actions by way of which reward (for deeds) are increased–Imaam Sadi (rahimahullaah)
بِسۡمِ ٱللهِ ٱلرَّحۡمَـٰنِ ٱلرَّحِيمِ
What are the means and actions by way of which reward (for deeds) are increased?
As for the increase of reward for a good deed to ten times the like thereof, this has to occur in every righteous action just as Allaah (The Most High) said: [مَن جَآءَ بِٱلۡحَسَنَةِ فَلَهُ ۥ عَشۡرُ أَمۡثَالِهَاۖ ] ”Whoever brings a good deed (Islamic Monotheism and deeds of obedience to Allah and His Messenger) shall have ten times the like thereof to his credit.”  As for the increase beyond this, which is what the questioner intends (in his question), it has its means: [a] It is either connected to the performer of the deed or the deed itself; and [b] It is either connected to the time (in which the deed is performed) or the place, or its (good) outcomes.
And from the most important means of increasing (the reward for good deeds) is when a slave actualises sincerity to Allaah and adherence to the way of the Messenger in his deeds. So (this increase occurs) when a deed is from those deeds legislated (in the sharia) and the slave intends by way of it the Pleasure of Allaah and seeking His Reward, and (when) this intention is firmly established as the urge towards the deed and the goal behind it, such that his deed is (carried out) due to his belief in Allaah and His Messenger; and (when) the urge behind (his deed) is due to (responding) to the command of Allaah and his aim is to seek the Face of Allaah and His Pleasure, just as the meaning of (these affairs) have been mentioned in a number of Aayaat and Ahaadeeth, such as the saying of Allaah (The Most High): [إِنَّمَا يَتَقَبَّلُ ٱللَّهُ مِنَ ٱلۡمُتَّقِينَ ] ”Verily, Allah accepts only from those who are Al-Muttaqun.”  That is: Those who fear Allaah in their deeds by actualizing Ikhlaas (sincerity to Allaah) and Mutaaba-ah (adherence to the path of the Messenger). And likewise, the Messenger (sallal-laahu-alayhi-wasallam) said: ”Whoever fasts the month of Ramadhaan, his previous (minor) sins will be forgiven”; ”And whoever stands (in the night prayer) during Ramadan out of Imaan and seeking reward (from Allaah), then all of his previous (minor) sins will be forgiven;”  and other texts besides these.
Therefore, a few deeds accompanied by complete sincerity carries much greater weight, which cannot be reached (i.e. through deeds accompanied by a weaker strength in sincerity even if they are numerous). And because of this, the apparent actions have more virtue over one another in the presence of Allaah due to the Imaan and sincerity established in the hearts. Also abandonment of what the soul desires of forbidden desires is included in those righteous actions that have virtue over one another due to the different levels of sincerity–and that is when a (person) sincerely abandons them from the bottom of his heart and not out of other than sincerity. The story of the companions of the cave (i.e. in soorah Kahf) is a witness to this. 
 Minor sins forgiven when one fasts the month of Ramadhaan, see article on this link: http://salafitalk.net/st/viewmessages.cfm?Forum=11&Topic=6255
 Al-Fataawaa As-Sadiyyah. Page: 43. Slightly paraphrased]