This month—Shabaan—is the prime time to start fasting those extra fasts or making up your missed fasts from last Ramadan.
Usamah ibn Zayd (may Allah be pleased with him) said: I said, 'Oh Messenger of Allah, I do not see you fasting in any other month like you fast in Shabaan.' He said, 'That is a month to which people do not pay attention, between Rajab and Ramadan, and it is a month in which deeds are lifted up to the Lord of the Worlds. I like for my deeds to be lifted up when I am fasting.'" (Narrated by al-Nasaai)
The best way to prepare fasting for a whole month is to start fasting often, in order to gain control over your actions, stomach and desires.
Fast Mondays and Thursdays:
Abu Hurairah reported that the most the Prophet (pbuh) would fast would be Monday and Thursday. He was asked about that and he said: "The deeds of people are presented to Allah on every Monday and Thursday. Allah forgives every Muslim except for those who are deserting each other." (Hasan)
Fast the White Days—13th, 14th and 15th of each Islamic month:
Abu Tharr Al-Ghefari said: "The Messenger of Allah (pbuh) said, 'Oh Abu Dharr! If you fast three days of every month, then fast the 13th, 14th and 15th (these are called Al-Ayaam Al-Beedh, the White Days).'" (Sahih)
The Prophet said, "(Allah said), 'Every good deed of Adam's son is for him except fasting; it is for Me, and I shall reward (the fasting person) for it.' Verily, the smell of the mouth of a fasting person is better to Allah than the smell of musk." (Bukhari)