1. Most (no ‘of’) is a determiner. For example it replaces a, an, the, every, some etc. in a sentence, so:
- ‘Milk in most supermarkets is cheap.’ OR, you could say, ‘Milk in the supermarket is cheap.’
- ‘Most people in England watch TV.’ NOT ‘Most of people in England watch TV.’
2. Most of (with ‘of’ ;-)) is a pronoun which refers to I, you, he, they, it, this etc. somewhere else in your writing or speech, so:
- I went on holiday last summer. I spent most of it relaxing and doing nothing.
- I spent most of the winter on the coast.