Most and Most of

If you're referring to a noun in general, you should not use most of.

  • Most English learners often make this mistake.

When referring to a specific noun, we add of.

  • Most of my students did this mistake during their test.

What does it mean "in general" and "specific"?

Well, in fact it all comes down to whether or not most is directly followed by a noun (or a noun + an adjective).  If it is — no the, my or whatever — then you're talking about a noun in general. Words such as my, the, those, these and so on modify the noun, therefore making it "specific".