The Qur'an is explicit when it comes to prayer in ways that the Christian Bible is not. There are definite reasons to pray: Qur'an 17:79 offers a bribe: pray often, more than is required of you, and Allah might "raise you to a position of great glory". Aside from that, the vast majority of the verses in the Qur'an about prayer are about technicalities - frequency, timings and posture. For example Qur'an 2:238-239 says that the "middle prayer" (presumably, of the 5 daily prayers) is the most important. Qur'an 5:6 reiterates typical superstitions about cleanliness and washing before prayer (more so if you've touched women recently). It seems that when God spoke to the Hebrews it was insistent upon the minute specifics of animal sacrifice, but, it revealed to the writers of the New Testament that such textual literalism was an error, and distracted from the proper relationship with God. But, hundreds of years later, God is again getting involved with the minute particulars. Despite the attempts to be clear, there are many uncertainties as to how Muslims should pray and there are many different customs. Some complications arise from basic geography: the Qur'an was written by folk who thought the world was flat, so instructions like "face Mecca when you pray" seemed simple enough. But what about Muslims in Argentina, Alaska or Australia? To pray facing Mecca means angling yourself against the floor in a very strange way. Some Alaskan Muslims pray facing north, the shortest curved line to Mecca. Others pray facing South-East, the simplistic way you'd face if you use the Mercator map projection whilst forgetting that the world is more or less spherical. The entire spectacle of reading lengthy Muslim scholarly debate on how and when to pray is a worryingly pointless use of Human time in a literalist endeavour that is largely avoided if you admit that the authors of the Qur'an didn't quite manage to be clear, and the minor details aren't really the kind of the thing the ruler of the Universe should really be caring about, given the violent and immoral state of the world at large!
For comparison to Christianity and for notes on prayer across all religions, see:
Qur'an 17:107,110 says to weep as it adds to the humility, but don't pray loudly (nor be silent). Mumbling is the order of the day.
“Call on your Lord humbly and secretly; surely He does not love those who exceed the limits.”
This is the same as the Christian Bible's instructions to pray in private, as Jesus did. It seems that the monotheistic God - being omniscient (all-knowing) - does not require or endorse mass displays of piety, which too easily become bombastic public dramas rather than genuinely-felt acts.
Just before praying, Qur'an 3:191 mentions that those who remember Allah' while 'standing, sitting, and laying down' (some translations say 'laying down on their side') are 'men of sense' - it doesn't here mention women who pray. This gives a lot of options as to posture! 2:238-239 says that prayers can be performed on foot (or on a horse) if required, which therefore implies that prayers are best if not on the move. However 17:107,110 is more limiting and says that to pray, you have to fall down on your face.
Some say that Qur'an 3:43 gives instruction to bow down. But this is clearly just part of a sentence being addressed to Mary, "Mary, be obedient to your Lord; bow down and worship with the worshippers", or in most translations "with those who bow down". Although according to Qur'an 3:191 they could be standing, sitting or laying. If Mary represents women in general, Qur'an 3:43 at most instructs women to bow down with worshippers. Yet, against the Qur'an, many Islamic institutions separate women from men rather than have them pray with them.
Just to add to the confusion, don't forget that Qur'an 7:55 instructs believers to pray humbly and in secret/private. So perhaps women - and men - shouldn't bow down with anyone and Qur'an 3:43 does indeed apply only to Mary. What you do depends on which verses you choose to follow.
The Qur'an is a male-dominated book, delivered to men, and written only for men to read. Most the instructions are given to men alone. For example, Qur'an 5:6 explains how and when to wash before prayer. It says you have to wash if you've touched a women recently. This clearly makes no sense if ever read by a women. Such shortcomings result from the Qur'an being written in a male-dominated culture, clearly the male authors of the Qur'an simply encoded their local customs and misogyny into their (man-made) holy writings.
Qur'an 52:48-49 makes a few unclear comments, saying to "keep up prayer from the declining of the sun till the darkness of the night and the morning recitation; surely the morning recitation is witnessed. And during a part of the night, pray Tahajjud beyond what is incumbent on you; maybe your Lord will raise you to a position of great glory". Derived from these and other equally ambiguous verses there are various interpretations as to when you should pray:
Qur'an 73 opens with commentary that the recital of the Qur'an is to be a chant. And, at night-time voice impressions are strongest and more eloquent than during the day, when daytime business distracts people (Qur'an 73:1-7). Although, Qur'an 73 may well be addressed solely to Muhammad, as it warns "We are about to address to you words..." (73:5), so it may just be night-time was the best time for the angels to address Muhammad, the Qur'an is nonetheless asserting the general principal that, despite tiredness and the like, night-time is a clearer time to chant the Qur'an. Or perhaps, Muhammad was an epileptic (or he suffered from a form of sleep apnea), and had more frequent visions at night-time, hence, the belief and assertion that the night-time was the best time for receiving and reciting the Qur'an.
An example prayer is given in Qur'an 3:191-194:
“Our Lord! You have not created this without purpose, glory to You! Give us salvation from the torment of the Fire.
Our Lord! Verily, whom You admit to the Fire, indeed, You have disgraced him; and never will the Zalimun [polytheists and wrong-doers] find any helpers.
Our Lord! Verily, we have heard the call of one calling to Faith: 'Believe in your Lord,' and we have believed. Our Lord! Forgive us our sins and expiate from us our evil deeds, and make us die (in the state of righteousness) along with Al-Abrar [the pious believers of Islamic Monotheism].
Our Lord! Grant us what You promised unto us through Your Messengers and disgrace us not on the Day of Resurrection, for You never break your Promise.”
An Islamic prayer
In Qur'an 3:191
Muslims pray facing Mecca as a symbolic gesture of Muslim unity. It is based on a historical pagan cultural phenomenon (alongside walking around the Qa'ba clockwise) adopted by early Islam. In the following verses from the Qur'an, the "qiblah" is the Arabic for the sanctioned direction of prayer.
"We have certainly seen the turning of your face, [O Muhammad], toward the heaven, and We will surely turn you to a qiblah with which you will be pleased. So turn your face toward al-Masjid al-Haram. And wherever you [believers] are, turn your faces toward it."
"From whatsoever place thou issuest, turn thy face towards the Holy Mosque
The authors of the Qur'an captured a time in Muhammad's life when the direction was changed from Jerusalem to the Holy Mosque at Mecca. The verse above was the setting of the new direction, and it was preceded by the abolition of the previous direction, as a test to see who would comply:
"And We did not make the qiblah which you used to face except that We might make evident who would follow the Messenger from who would turn back on his heels. And indeed, it is difficult except for those whom Allah has guided."
According to this verse, in order to make it evident, God declared this change of prayer direction. But it says in the Qur'an many times that God is all-knowing, and therefore, God knew in advance who would comply, and who wouldn't. And in fact, it says that God itself guided those who passed the test. So the whole reason of "making it evidence" contradicts (1) god's omniscience (it knew who would comply, so, no test was needed) and (2) god's omnipotency (it itself guided those who passed, so no test was needed).
The Complications of a non-Flat Earth
When written, it seems relatively simple that Muslims should all face Mecca. In a flat world, it is just a matter of knowing which way to orient yourself when you pray. The cruel world turned out to be almost spherical, and the question of direction has become very vexing. It is easy in the Middle East to use a compass (or the sun) to ascertain the direction. But there are four problems:
Because the Earth isn't flat, there are multiple directions you can face when "facing Mecca". In the USA, you could face either East or West (generally) and be facing Mecca.
On a spherical Earth in many places such as Alaska the closest direction to Mecca is to look over the poles, but, traditional Islamic star-gazing recorded relatively equatorial star positions, therefore, traditional methods have Muslims facing Mecca the long way round in many circumstances.
Because the Earth is spherical, if you are in Argentina and you lay facing North East, you are not facing Mecca at all. The curve of the Earth means you are facing out into the far reaches of space. To face the Earth from Argentina you have to angle yourself at 30 degrees towards the floor. Then you are oriented to Mecca.
Finally, the Qur'an says "turn your face" to Mecca. This means that the traditional position of praying face-down has most Muslims not facing Mecca at all. They are oriented to Mecca, for sure, but they are not facing it.
These problems are as ridiculous as they are trivial because it is clear to all that the authors of the text of the Qur'an didn't understand the geography of a curved Earth. The solution is to admit the cause of the problem, and to adapt the verses so that they make practical sense. In reality this is what Muslim authorities actually do. They come to practical solutions. It doesn't matter if the rules don't always make sense, what matters is a Muslim togetherness of purpose and the distinctive communal appearance of Muslim directioned prayer.
In reality, this practical-minded approach trumps scripture, because Muslim authorities know that the underlying text is not suited to a curved world. The famous instructions to a Muslim astronaut aboard the International Space Station was to pray facing Mecca if they could see where it was, or failing that, to pray facing the Earth in general (which I find to be a lovely sentiment), or failing that, to pray facing "wherever"2 because at the end of the day, it is literally the thought that counts, not the inane specifics. If only the same logic applied to the rest of the Qur'an!