The Quran says those who repent are forgiven. (66.8)
Tawbah literally means to return. Scholars have laid down three conditions for tawbah. In English, tawbah is translated as introspection or repentance. 
There are three conditions for tawbah. The first is النَّدَمُ توبة or repentance. 
You should feel intensely that you have made a mistake. The hadith says: النَّدَمُ توبة (Sahih Ibn Hibban 612) The reality of tawbah is repentance.
The second is to take the pledge to not make the mistake again. This is to feel ashamed and firmly resolve to not repeat the mistake. Once was enough. The third condition is that if it is a matter relating to another person, for example, if I have unjustly taken his money, I must return it. If I have wounded him, I must provide him medical assitance. This is compensation. We cannot compensate when the mistake relates to God. But when it involves another human being, we have to do compensation. 
There are three conditions for tawbah: The first is repentance. The second is to be determined not to make the mistake again and to seek God's forgiveness. The third condition is that if I have done something against a human being by making him suffer a loss, I must compensate for it. These are the three conditions. If you fulfil these three conditions, the Quran clearly says that God will forgive you.