Hadhrat Abu Bakr Katani (May Allah shower His mercy on him) says: Repentance is a Noor and Tauba is a name with 6 meanings in it:
1. To be remorseful about past sins.
2. To make a firm decision not to sin again.
3. Making up those obligations (Faraaidh) which were not performed.
4. Fulfilling the rights of the creation, which were not fulfilled or exploited.
5. To break down the flesh and fat, which were created through Haraam in the body.
6. Taxing the body through worship, the way it experienced pleasure in sin.
The 4 pillars of Tauba:
Hadhrat Hasan Basri (May Allah shower His mercy on him) says: Tauba has 4 pillars:
1. To recite Istighfaar (i.e. repent) with the tongue.
2. To be remorseful in the heart.
3. To save the body parts from sins.
4. To have the intention in the heart of not repeating the sin.
Tauba of different body parts/organs:
Hadhrat Dhun Nun Misri (May Allah shower His mercy on him) says:
1. The Tauba of the heart is to make the intention (Niyyah) of abandoning the Haraam and forbidden things.
2. The Tauba of the eye is to not see the things, which are forbidden.
3. The Tauba of the ears is to not listen to forbidden and indecent things.
4. The Tauba of the hand is not to extend the hand towards forbidden things.
5. The Tauba of the legs is to not go towards forbidden places.
6. The Tauba of the stomach is to not eat forbidden things.
7. The Tauba of the private parts to stay away from adultery and fornication.
[From Mawaiz-e-Hasana of Hadhrat Muhaddith-e-Deccan]