(I'm writing a book based on this topic (Repentance) in which I will insh'Allah make the Muslim youth (myself included ) understand how important repentance is for a believer. Please share the story with family and friends. I haven't posted a chapter yet but only an introduction. The first chapter will be up soon insh'Allah. The story is on my main account  @HijabQueen_22,  the book is  called  Repentance )

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A person can ask Allah to forgive him for his sins (or a sin), in general, by simply doing Istighfaar. Istighfaar - seeking forgiveness from Allah. So it is simply saying the phrase Astaghfirullaah (I seek Allah's forgiveness)". أَسْتَغْفِرُ اللَّه This Istighfaar can (and should) be done anytime and anywhere, whether it's after prayer, before sleeping, after waking up or simply whenever one wants to say it. 

We also know that when an individual prays the five daily prayers, fast Ramadan and attend the Friday (Jumu'ah) Prayer, all of our minor sins are forgiven through them. Just by doing these simple acts, our sins are being forgiven... SubhanAllah. One thing we should also put into practice is sitting down for a few minutes after Salat remembering Allah and say Subhaanallaah (High is Allah above every imperfection & need; He is pure and perfect) 33 times, and Alhamdulillaah (All praise be to Allah) 33 times and Allaahu Akbar (Allah is the greatest) 34 times .

One thing I suggest when repenting is to shed tears and say what you've done wrong to Allah, what you would do to make yourself a better Muslim and promise Allah that you wouldn't repeat the sin again. 

I personally think shedding tears help you because you will be able to see how much the sin has affected your soul and it's like your cleanse your soul when you cry. 

(As soon as an individual sin,  it is best if he or she seeks forgiveness from Allah straight away.  Because...)