Almost invariably it happens a few days after the end of Ramadan. The letdown. Fasting is finished; the nightly prayers are over; the group gatherings to break the fast have vanished. We can eat, drink, and be merry again when the sun is shining. And that special feeling you have in your heart--the one that keeps you going despite your hunger and thirst--gradually fades away. The spiritual high evaporates, and all you are left with are the bad habits you tried to shed during Ramadan, but mysteriously rear their ugly heads once it is over.
Ramadan is supposed to increase your faith and God-consciousness: Believers! Fasting has been prescribed for you--as it was prescribed for those before you--so that you may be conscious of God. (The Holy Qur'an, 2:183). The point is not to be an angel for Ramadan and a demon at other times. The lessons learned and spiritual benefits gained during that month are intended to carry over for the rest of the year until next Ramadan.
Yet frequently they do not. Is there anything we can do about it? Absolutely, and here are five ways we can try to keep the spirit of Ramadan alive and well throughout the rest of the year.
Keep up the good habits practiced during Ramadan.
More than just denying oneself food and drink, the fast of Ramadan is a complete body-and-soul fast. Although this should be the behavior of the believer at all times, when one is fasting, he or she should take special care not to harm anyone, curse anyone, or do anything wrong.
In fact, the Prophet (pbuh) said: "Whoever does not give up forged speech and evil actions [while fasting], God is not in need of his leaving his food and drink." Well, once Ramadan is over, these good behaviors should continue.
For instance, if you took the opportunity of the month of Ramadan to try to curb talking about other people, why not continue to refrain from doing so after Ramadan is over? We should continue to go to the mosque for congregational prayers. It is so amazing to see the mosque--which was packed just a few days earlier--stand almost completely empty during Isha, or night, prayers, after Ramadan. If we can go to the mosque each day during Ramadan, we can get there  every day during the rest of the year. 
Smoking is prohibited during daylight hours during Ramadan, which makes it the perfect opportunity to quit cigarettes. Yes, the nicotine in tobacco smoke is more addictive than heroin, and it is one of the most difficult addictions to beat. But if you can go without smoking for 14-17 hours a day during Ramadan, you can go without it for the remaining 7-10 hours. Ideally, there should be no Muslims who smoke, given the fact that they have to stop doing so for most of a month every year. Sadly, the reality is quite different. Many, many Muslims smoke, and it saddens me--especially since I am a lung specialist who sees firsthand the devastation wrought by cigarette smoking--to see groups of men outside the mosque immediately light up the moment sunset arrives.
Continue to fast throughout the year.
I must admit that this is the most difficult one for me to follow, but I must mention it anyway. The fast of Ramadan is obligatory for every adult Muslim, but there are numerous other fasts that Muslims are encouraged to undertake throughout the year, and we should try to participate. For instance, the Prophet Muhammad (pbuh) encouraged Muslims to fast six days of the month of Shawwal, the month after Ramadan. The reward is equivalent to fasting the entire year. In a few months, the season of Hajj will begin, and those Muslims who do not perform the Hajj are encouraged to fast the day of Arafat, when all the pilgrims will be standing on that plain and begging God for forgiveness. We should fast that day. For Ashura, the day that commemorates the exodus of the Children of Israel from Egypt (and, for Shi’a, the murder of Imam Hussein, the Prophet's grandson), Muslims are encouraged to fast that day as well as the day before. (Ideally, Muslims should fast the first ten days of the month of Dhul Hijjah, when the Hajj occurs.)
For the very ambitious, the Prophet (pbuh) used to fast every Monday and Thursday, and if one is able, he or she could follow this sunnah, or tradition of the Prophet (pbuh). The very, very ambitious could even fast in the tradition of the Prophet David (pbuh): fasting every other day. If this is too much, perhaps we can fast one, two, or three days each month.
Whatever the number, we should try to fast outside of Ramadan to help keep the spirit of the month alive in our daily lives. (As I said, this is perhaps the most difficult suggestion for me--I have a hard time fasting outside of Ramadan.)