How can one prevent other thoughts from occurring while chanting?

Just as sugar has sweetness as its quality, so also the nature of the mind is to think continuously or to harbour a certain emotion arising from some thought. In the beginning when chanting, everyone gets various thoughts due to the impressions from previous births.

Which Name should one chant if the Guru has not imparted a Name?

One should repeat (chant) the Name of the family deity (kuladevata), which refers to both the male or the female family deity. Depending upon which family deity’s worship is conducive for his spiritual progress, an individual is born in that particular family.

Namsankirtanyoga

Uniting the embodied soul with Supreme God through the medium of chanting the Name of the Deity is known as Namsankirtanyoga.