People commemorate and show respect to their ancestors by visiting their graves, offering food, tea or wine, burning incense, burning or offering joss paper (representing money), etc. They sweep the tombs, remove weeds, and add fresh soil to the graves.
People pray before their ancestors' graves and beseech them to bless their families.
As an alternative to burning incense or joss paper, a more eco-freindly way to worship ancestors on Tomb Sweeping Day is to pray for them. It is also a more effective way to send them what they need, for prayers are not limited by time and space.