{Indeed We revealed it on the Night of Qadr (Decrees). And what will convey unto you what the Night of Qadr (decrees) is? The Night of Qadr (decrees) is better than a thousand months. The angels and spirit descend therein by the permission of their Lord with all decrees. (The Night) is Peace until the Dawn.} [Al-Qadr 99]

2. It is also the Night when all ordainments for the year are decreed. Allah (T) said, which means:

{By the manifest Book (the Quraan) that makes thing clear. We sent it (this Quraan) down on a Blessed Night (i.e. the Night of Qadr) in the month of Ramadaan. Verily We are ever warning [mankind that Our Torments will reach those who disbelieve in Our Oneness of Lordship and in Our Oneness of Wordship]. Therein (that night) is decreed every matter (amran) of ordainment} [The Smoke 44:2-5]

"Amran" (i.e. a command, or this Quraan, or the Decree of every matter is) from Us.

Its time
It is established in the Sunnah that knowledge of this glorious night was taken away from this Ummah due to quarreling between two Sahabas.

Ubaadah ibn Saamit said: ""The Prophet (S) came out with (information about) the night of Qadr (Decrees); two men from among the Muslim were quarreling and he said: "Verily I came out to inform you about the night of Qadr but such and such person were quarrelling so it was raised. and maybe this is good for you. However, search for it in the ninth, the seventh, and the fifth." [Bukhaaree]
The most authentic report on this issue is that Lailatul Qadr (the Night of Decrees) should be sought during the odd nights of the last ten nights of Ramadaan. Aa'ishah relates that the Messenger (S) of Allah (T) used to perform I'atikaaf during the odd nights of the last ten nights of Ramadaan and he (S) said: "Seek for the night of Qadr (decrees) during the odd (nights) from the last ten (nights) of Ramadaan." [Al-Bukhari and Muslim]
If there is weakness or inability to search in the odd nights of the last ten nights, then the Muslim should try not to miss out the odd nights of the last seven nights as is established in the following Hadeeth.

Ibn'Umar narrates that the Messenger (S) of Allah (T) said: "Seek it in the last ten Nights. However, if one of you becomes weak or is not able to, then let him not be subdued by the last seven nights." [Bukhaaree and Muslim]

Summary: There are different opinions relative to what night is the Night of Qadr (decrees) but the best thing for the Muslim who is sincere in seeking it, is to search for it during the odd nights of the last ten nights. If he is not able to or weak, then he should at least seek it on the 25th, 27th and 29th night. And Allah knows best.

How should the Muslim establish this Night?
Indeed this Night, because of its sacredness, should be something that the sincere Muslim strives to seek after; by establishing its odd nights with Eemaan (i.e. performing prayer) and a desire to accrue for himself its blessing. If he achieves this, then all his previous sins will be forgiven as is established in the following Hadeeth. The Messenger (S) said: "Whoever prays the Night of Qadr (Decrees) with Eemaan (faith) and hoping for its reward, Allah will forgive him all his previous sins." [Bukhaaree and Muslim]

During this night also it is recommended to make dua'a as much one possibly can. It is narrated from Aa'isha (R) that she said: "I said: 'O Messenger of Allaah, if I know what night is the Night of Qadr what should I say?." He said: "Say: O Allaah you are pardoning and you love to pardon so pardon me. " [Ahmad,Ibn Majah,Tirmidhee]

Now that you are aware of the night of the Qadr, establish the last ten nights and enliven it with Ibaadah and abstain from your women and encourage your family to do the same and do obedience during it as much as you are able to.

Aa'isha (R) said: "When the last ten days of Ramadaan arrived the Messenger (S) used to abstain (from contact a with his wives) and he would establish the nights. He would awaken (his family) to do the same also." [Bukhaaree and Muslim]

And she(R) also said: "The Messenger of Allaah (S) used to strive in Ramadaan more than he did in any other month." [Muslim]

The Signs of the Night of Qadr.
The Messenger of Allaah (S) described the morning of the night of Qadr so that the muslims can know which night it is.

Ubayy (R) said : "On the morning of the night of Qadr the sun would rise without any beams; (it is like) a wash basin until it raises." [Muslim]