A person should be careful not to lie down to sleep before having recited the Shema in the correct way, and when praying the evening service before nightfall he has not fulfilled the obligation of reciting the Shema until he recites it again in the correct way after nightfall. One must be careful of the above because many times a person will lie down to rest a little and thinks that he will not fall asleep and then he is overcome by sleep and remains without having recited the Shema whereby he destroys much goodness. Chazal say that one who does not recite the Shema or recites it at the wrong time should be excommunicated. Similarly, one must pay attention to the time for reciting the Shema in the morning as there are many people who in the summer months are lazy and like sleeping in (especially on Shabbos, festivals, celebrations and happy times) and in many cases they miss the final time for the recital of the Shema. A man who is G-d fearing will recite it early in the morning.
One must be very accurate with the enunciation of the letters of the Shema. This can only be achieved by reciting it slowly and carefully and spending a lot of time to become accustomed to doing this. It is correct to strengthen oneself to give pleasure to our Creator as Chazal say that one who takes pains to say the letters correctly will have the fires of Gehinnom cooled down for him. This is a great goodness.