It is recommended (sunnah) to break one’s fast as soon as one is sure the maghrib (sunset) has begun.
It is good to break one’s fast by eating dates, and if not available, then by drinking water. It is good to say the following statement upon breaking one’s fast:
اللهم لك صمت وعلى رزقك أفطرت
which means: <<O Allah, for Your sake I fasted, and with Your sustenance I broke my fast.>> It was narrated from Abu Dawud that the Prophet used to say this supplication upon breaking his fast. It is also good to delay the suhur meal until a time close to the dawn--but to stop eating before the dawn.
Refraining from backbiting, cursing a Muslim, and other sins, is more emphasized while fasting. In committing some sins, the reward of one’s fasting might be lessened or lost. If someone curses another, let the one cursed abstain from responding with a similar curse. Instead, let him say, “I am fasting. I am fasting.”