Some mistakes:
1. Du'aa containing aspects of shirk in worship (i.e invoking others or other along with Allah subhanahu wa ta'ala).
'O young man, I am going to teach you some words: Be mindful of Allah, and He will be mindful of you. Be mindful of Allah, and you will find Him before you. When you ask, ask Allah. When you wish to seek help, seek help from Allah. Remember that if all the people come together to bring you benefit they cannot benefit you except what Allah has written. On the other hand, if they come together to cause (you) any harm they will not be able to do it except for what Allah has written. The pens have been laid aside, and the scrolls have dried.' (Narrated by al-Tirmidhi who declared it Hasan Sahih).
2. Forbidden types of tawassul
That he makes tawassul to Allaah in his du`aa by the honour of the Prophet or his sanctity, or his blessing, or by the honour of those besides him from the Saaliheen, or their sanctity or their right or their blessing, so he says, by way of example, "O Allaah, by the honour of your Prophet, or his sanctity, or his blessing, give me wealth and offspring or enter me into Paradise and save me from the Fire", then he is not a Mushrik with the major shirk which expels him from Islaam, but it is forbidden in order to close the means (leading) to Shirk and in order to distance a Muslim from doing anything that leads towards Shirk. And there is no doubt that tawassul through the honour of the Prophets and righteous is one of the means of Shirk, that eventually lead to it after the passing of days (i.e. time), according to what has been indicated by (practical) experience and what the reality testifies to... (Fataawaa Lajnah ad-Daa'imah, (1/338), [Check
Here for further resources]
3. Dua asking for Death
The Prophet (peace and blessings be upon him) said,
"No one should wish death for any affliction that has befallen him. If he finds his situation unbearable, let him pray: "Allahumma ahyini ma kanati al-hayatu khayran li wa tawaffani ma kanat al-wafatu khayran li (O Allah, grant me life if life is good for me, and grant me death if death is good for me)." (Muslim)
Imam Ahmad reported that Anas said,
“Allah’s Messenger visited a Muslim man who had become as weak as a sick small bird. Allah’s Messenger said to him, `Were you asking or supplicating to Allah about something’ He said, `Yes. I used to say: O Allah! Whatever punishment you saved for me in the Hereafter, give it to me in this life.’ Allah’s Messenger said:
((All praise is due to Allah! You cannot bear it -or stand it-. You should have said: (Our Lord! Give us in this world that which is good and in the Hereafter that which is good, and save us from the torment of the Fire!))
The man began reciting this Du`a and he was cured.” Muslim also recorded it.
5. Invoke for something fobidden or a sin,
for e.g, asking Allaah to make some one as drug addict or asking Allaah that someone to die as kafir e.t.c
6. Severing ties of kinship,
7. As a way of testing Allah's Power, response etc,
8. Abandoning du'aa due to despair
'The servant's du'a will be answered provided he does not ask for what is sinful or for the breaking off of relations, and also if he does not show impatience.' He was asked, 'O Messenger of Allah, what is impatience?' And he replied, 'That the servant says: "I invoked, but I do not think it (my invocation) was answered", and he becomes disappointed and abandons du'a.' (Narrated by Muslim in his "Sahih" from Abu Hurairah).
9. Excessiveness in raising voice
'Be kind to yourselves for you are not calling upon One who is deaf or absent. You are calling upon One who is All-Hearing and All-Seeing.' (Bukhari & Muslim reported it from Abu Musa).
10. You should'nt ask Allah to make His decree that is bad for you, easy for you but rather Allah should ward it off.
Ask with absolute resolve, and believe with certainty that your du'a will be answered. The Prophet (salallahu alayhi wa sallam) said: 'When one of you makes du'a he should not say, 'O Allah, forgive me if You wish, have mercy on me if you wish, give me provision if you wish,' but he should ask with resolve because he does what he likes; no one can force Him.' (Bukhari)
The Prophet (sallalahu alayhi wa sallam) also said: 'Ask Allah subhanahu wa ta'ala when you are sure of His response, and remember that Allah does not accept the du'a of the unmindful and neglect heart.' (Declared Hasan by Sheikh Al-Albani in "Silsilah al-Ahadith Al-Sahihah" no 594)
12. Invoke Allah against oneself, property, wealth or family :
Jabir (radhiAllahu 'anhu) said the Prophet (salallahu alayhi wa sallam) said:
'Do not make du'a against yourself, nor make du'a against your children, nor your property, for your du'a may coincide with the time when Allah grants all supplication, and your du'a might be granted (and cause you harm).' (Muslim).
