What should a person do for their past and future sins to be forgiven?

There are authentic hadiths that mention deeds by which past sins are forgiven, such as fasting Ramadan (definition) and praying during its nights (qiyam (definition)), praying during Laylat al-Qadr, performing ablution and two rak'ahs of prayer without obsessive thoughts (waswasah), one's ameen coinciding with the Imam's or saying "Allahumma Rabbana wa lakal-hamd" (O Allah, our Lord, and to You be praise) coinciding with the ameen of the angels, saying "Alhamdulillah Alladhi at'amani hadha wa razaqanihi min ghayri hawlin minni wala quwwah" (Praise be to Allah who fed me this and provided it for me without any power or strength from me) after eating, and an accepted Hajj. These deeds expiate minor sins, not major ones. Major sins are not forgiven except through repentance or Allah's mercy. Sincere repentance (tawbah (definition) nasuh) is the greatest cause of forgiveness, and one who repents from a sin is like one who has no sin.