HOW TO DO TOBAH (Repentance)

If one have committed sin and you want to repent, Then Promise ALLAH not to do this again , if by chance you committed this sin again then again pray like this.
 
INSHALLAH YOUR TOBAH WILL BE ACCEPTED BY ALLAH.
HOW TO KNOW THAT MY TOBAH WAS ACCEPTED?
If i was taking interest then i left it and did TOBAH, if i see some on taking or dealing with interest i should get sad , interest is haram i was also taking it OH ALLAH forgive me.it means your TOBAH is accepted.
If i will tell hay i was dealing with INTEREST ,i used to get loan in lacks ,or i am happy from my past, that mean TOBAH has not accepted.
AND ALLAH KNOWS BEST.