How to Improve Your Character in Islam
Question

I have a very bad character; I am disobedient and defiant towards my mother and I often make her angry. Sometimes my manners and character are good, but most of the time they are bad. How can I improve my character and my manners? What are the things that will help me to be kind to my parents and develop a good character? Will I be punished if my character and manners are bad? Or is having a good character something that is only good but is not essential? When my character is good, I feel that I am showing off, and I feel that I am committing minor shirk (by showing off). So how can I remain steadfast in having a good character and good manners, whilst being sincere to Allah in that regard?
Praise be to Allah.Virtue of a good charecter in Islam
A good character is something that will weigh most heavily in the balance of deeds on the Day of Resurrection, and the best of people in character will be seated closest to the Messenger of Allah (blessings and peace of Allah be upon him) on the Day of Resurrection.
It was narrated by At-Tirmidhi (2018) – who classed it as sound – from Jabir (may Allah be pleased with him) that the Messenger of Allah (blessings and peace of Allah be upon him) said: “Among the dearest of you to me and those who will be seated closest to me on the Day of Resurrection are those of you who are best in character .” (Classed as authentic by Al-Albani in Saheeh At-Tirmidhi)
Al-Bukhari (6035) and Muslim (2321) narrated from ‘Abdullah ibn ‘Amr (may Allah be pleased with him) from the Messenger of Allah (blessings and peace of Allah be upon him) that he said: “The best of you are the best of you in character.”
An-Nawawi (may Allah have mercy on him) said:
“This is encouragement to have a good character, and it highlights the virtue of such a person, for this is the character of the Prophets of Allah, may He be exalted, and His close friends (Awliya’).”
Al-Hasan Al-Basri (may Allah have mercy on him) said:
“The definition of a good character is doing acts of kindness, refraining from causing harm, and having a cheerful countenance.”
Al-Qadi ‘Iyad (may Allah have mercy on him) said:
“It means mixing with people with a kind and cheerful character, and being friendly and compassionate towards them, putting up with them, showing forbearance and patience towards them at times of hardship, refraining from being arrogant towards them or mistreating them, and avoiding being harsh and angry with them or being critical towards them.”
Is it a sin to disobey your parents?
Defiance and disobedience towards parents is a major sin , and the one who is defiantly disobedient towards his parents will not prosper in this world or in the hereafter.
What the Muslim, man or woman, must do is treat his parents very kindly and strive to treat them well in every way possible, and to avoid angering them or going against their wishes and defiantly disobeying them.
How to improve your character in Islam
It is possible to improve one’s character and refine it, by doing the following:

Knowing the virtues of having a good character and the reward that will result from it in this world and the hereafter.
Knowing the bad consequences of having a bad character, and what will result from it of requital and negative consequences.
Studying the biographies of the earlier generations (Salaf) and the lives of the righteous.
Avoiding getting angry, striving to attain patience, and training oneself to be deliberate and not hasty.
Sitting with people of good character, and avoiding sitting with people of bad character.
Training oneself to develop a good character and trying to make oneself become accustomed to that, and being patient when striving to do that.
Finally: calling upon Allah, may He be Exalted, and asking Him to make your character good and help you to attain that. One of the supplications of the Prophet (blessings and peace of Allah be upon him) was: “O Allah, You have made my outward appearance good, so make my character good.” Narrated by Ahmad (24392); classed as authentic by the commentators on Al-Musnad. Also classed as authentic by Al-Albani in Sahih Al-Jami‘ (1307).

If a Muslim slips and behaves badly in some situation, he should hasten to apologise and set things straight, and he should resolve to improve his character.
When the Muslim strives to improve his character, doing that in obedience to the command of Allah, may He be exalted, seeking His pleasure and following the example of the Messenger of Allah (blessings and peace of Allah be upon him), this is like any other act of worship (that is, he should be sincere in his intention and so on). So he should not try to improve his character in order that people might praise him, because this will cancel out the reward and he will be deserving of punishment for showing off.
Just as the Muslim should strive to make all his worship sincerely for Allah alone, so too he should strive to do the same when trying to improve his character. He should always bear in mind the command of Allah, the reckoning, the balance, and paradise and hell, and he should remember that people will never benefit him or harm him at all. Remembering the hereafter is one of the most important means that will help the Muslim to be sincere to Allah, may He be exalted.
How to be dutiful to parents in Islam?
Things that will help one to treat parents kindly include the following:

Knowing the rights and virtues of parents, and how they brought up their children and put up with hardship in order to give their children a life of ease and joy.
Knowing the Islamic texts that encourage showing kindness to parents , and the texts that warn against defiantly disobeying them, and understanding the effect that it may have and the punishment for it in this world and the hereafter.
Knowing that showing kindness to parents is one of the greatest means of ensuring that the one who shows kindness to his parents will have children who will show kindness to him, and that defiantly disobeying parents is one of the greatest means of ensuring that the one who defiantly disobeys his parents will have children who will be defiantly disobedient towards him.
Studying the biographies of the earlier generations (the Salaf) and learning how they used to honour their fathers and mothers.
Reading books and essays that speak about showing kindness to parents or defiantly disobeying them, and also listening to Islamic lessons that speak about these topics.
Gifting them, saying kind words, being cheerful, offering a great deal of supplication and speaking well to them are among the greatest means that help one to show kindness to parents.

And Allah knows best.