Dua:
Dua (دعا) means to ask Allah (SWT) directly for something. There is nothing that Allah cannot do, therefore Dua is basically the means of asking the creator.
Islam encourages us to make a lot of dua, and not to be hasty in seeking a response. That is because dua’ is a great act of worship which is beloved to Allah. Indeed there are texts which warn us against neglecting dua’, because neglecting it is a sign of arrogance.
The Essence of Worship:
Allah says in Quran, And your Lord says, “Call upon Me; I will respond to you.” Indeed, those who disdain My worship will enter Hell [rendered] contemptible.” (Chapter 40 and Verse 60)
Hence, Allah asked His people to call out to Him. Additionally, Invocation is considered as the main essence of “Ibadat”.
Ask Allah to Grant His Blessings:
In Islam, Dua is termed as Supplication and Invocation; in which one humbly asks Allah to give something. One can ask something for himself/herself or on the behalf of someone other. For Muslims, supplication is a profound act of Allah’s worship. 
What a tragedy, for dua is the most potent weapon of a believer. It can change fate, while no action of ours ever can. It is the essence of worship. With it we can never fail; without it, we can never succeed. In the proper scheme of things, Invocation should be the first and the last resort of the believer, with all his plans and actions coming in between.
In every difficulty, our first action is dua, as is our last. We ask Allah to show us the way to handle that difficulty; we seek His help in following the path He shows to us; we seek His aid in making our efforts successful.
We should remember the Hadith:
“There is nothing dearer to Allah than a servant making dua to Him.”
We should make dua at all times, not only during times of distress. The Prophet Muhammad (Peace Be Upon Him) said:
“Whosoever desires that Allah answers his dua in unfavorable and difficult conditions, he should make plentiful dua in days of ease and comfort.”
Also, he said:
“The person who does not ask from Allah, Allah becomes angry with him.”
We should ask for all of our needs: those related to this world as well as those related to the Hereafter.
“The dua of a Muslim for his brother (in Islam) in his absence is readily accepted. An angel is appointed to his side. Whenever he makes a beneficial dua for his brother the appointed angel says, ‘Aameen. And may you also be blessed with the same.'” [Sahih Muslim]
“The supplication of every one of you will be granted if he does not get impatient and say, `I supplicated my Lord but my prayer has not been granted’.’’ [Saheeh Al-Bukhari, Saheeh Muslim]
It was narrated from Abu Hurayrah that the Messenger of Allaah (peace and blessings of Allaah be upon him) said: “(The du’aa’) of any one of you will be answered so long as he is not hasty in seeking a response and does not say, ‘I prayed but I have not had a response.’” (al-Bukhaari, 5981; Muslim, 2735 )
It was narrated from Abu Sa’eed al-Khudri (may Allaah be pleased with him) that the Prophet (peace and blessings of Allaah be upon him) said: “There is no Muslim who calls upon Allaah with words in which there is no sin or severing of family ties but Allaah will give him one of three things: either He will answer his prayer soon, or He will store it up for him in the Hereafter, or He will remove something bad from him that is equivalent to what he is asking for.” They said, “Then we should make a great amount of du’aa’.” He said, “Allaah is greater.” (al-Tirmidhi, 3573; classed as saheeh by al-Tirmidhi and others. )
What to Ask in Dua?
How to make supplication for something you really want? The two broad categories of what is asked include world and the religion. In Sahih al Bukhari, Hazrat Anas (May Allah be pleased with him) narrated:
“None of you should long for death because of a calamity that had befallen him, and if he cannot, but long for death, then he should say, ‘O Allah! Let me live as long as life is better for me, and take my life if death is better for me”
How to make Allah accept my Dua?
In order to get the status of “accepted for Supplication“, following conditions are to be met:
- Sincerity
- Tawassul
- Patience
- Purity
- Good intentions
- Attentive heart
- Sustenance
Ultimately, the faith that Allah will give when there is the right time as He knows all is the key to make Invocation accepted.
Ask Allah Only:
In Islam, Muslims can only pray to Allah. As written in surah 7 and ayah 197:
“But those ye call upon besides Him, are unable to help you, and indeed to help themselves”
Once the Prophet Muhammad (S.A.W) said:“Why don’t they make supplication to Allah for protection”
However, Dua is a conversation between a Muslim and Allah, in which one asks for His help and protection. It is the most powerful weapon to beat all the struggles in life and hereafter. But, it only works for who makes it with sincerity and faith.
Source: Wikipedia