We use some with of before the, demonstratives (this, that), pronouns (you, us) or possessives (my, your). We use some of to refer to a part of a whole:
I wasn’t sure about some of the answers.
It was great to meet some of her friends and colleagues.
Not: … some her friends …
[from a TV news programme]
First a look at some of today’s main stories in some more detail.