Prophet Muhammad (PBUH) was al-Insan al-Kamil, the most virtuous human being ever! Yet he used to ask Allah for forgiveness numerous times a day.  Obviously, seeking Allah's Forgiveness is something we should regularly do.
Question is, why should we seek forgiveness from Allah repeatedly?
We, as humans, are imperfect beings. We make mistakes, fall into error, and often go astray. Sometimes, we may make mistakes we are not even aware of! At other times, in trying our best to do good, we may end up causing harm. In all these situations, it is good to turn to Allah for forgiveness. He is the Ultimate Forgiver and it is only with His Help that we can overcome our faults.
Ask forgiveness from your Lord, verily, He is Oft Forgiving; He will send rain to you in abundance. And give you increase in wealth and children, and bestow on you gardens and bestow on you rivers.
I seek forgiveness from Allah, my Lord, from every sin I committed knowingly or unknowingly, secretly or openly, and I turn towards Him from the sin that I know and from the sin that I do not know. Certainly You, You (are) the Knower of the hidden things and the Concealer (of) the mistakes and the Forgiver (of) the sins. And (there is) no power and no strength except from Allah, the Most High, the Most Great.
Once Imam Ahmad ibn Hanbal (RA) was travelling. Eventually, he stopped by a town. He did not reveal his identity to anyone so that he wouldn't attract unnecessary attention to himself. Not knowing anyone in the town, he went to the local masjid intending to spend the night there.
However, the caretaker of the masjid failed to recognize him. He requested Imam Hanbal to vacate the masjid's premises. A baker whose shop was not far from the masjid witnessed this scene and felt sorry for the Imam. He invited Imam Hanbal to stay at his bakery for the night. The Imam accepted.
"And what is that (unanswered) Dua?" asked the Imam.
"To be able to see the famed Imam Ahmad ibn Hanbal!" was the reply.
Upon hearing that, the Imam introduced himself to the baker and informed him that all his prayers have been answered due to the virtue of him reciting "Astaghfirullah".
As a result, we should seek Allah's Forgiveness as often as we can. We are not perfect beings, but with Allah's Help, we can strive for betterment. Let us all try to develop a habit of reciting Astaghfirullah as much as possible.