During the last hours of the night i.e. just before dawn, offer 2 cycles of prayer and then recite this verse  21, 40 or 313 times with 7 times durood before and after. During recitation, just consider yourself as the most sinful person among the creations and imagine as you are sitting in wait for your Lord’s Mercy. You are seeking His forgiveness from all your sins with all your concentration and certainty that you are asking help from your Lord only with full devotion and concentration and you have to get forgiveness for all your sins.