We use the quantifier most to talk about quantities, amounts and degree. We can use it with a noun (as a determiner) or without a noun (as a pronoun). We can also use it with adjectives and adverbs to form the superlative.
Most with a noun
We use most with nouns to mean ‘the majority of’:
She plays tennis most mornings.
Most tap water is drinkable.
We don’t use the most with this meaning:
The sun shines over 800 hours during June, July and August and on most days temperatures rise above 25 degrees.
Not: … and on the most days …
When we are talking about the majority of something in general, we use most + noun. When we are talking about the majority of a specific set of something, we use most of the + noun.
Most desserts are sweet.
Desserts in general
The food at the party was delicious. He’d made most of the desserts himself.
A specific set of desserts (at the party)
When we use most before articles (a/an, the), demonstratives (this, that), possessives (my, your) or pronouns (him, them), we need of:
Most of the information was useful. Some of it wasn’t relevant.
Not: Most the information …
They sold most of their apartments quite quickly.
When there is no article, demonstrative or possessive pronoun, we don’t usually use of:
There hasn’t been much rain. Most rivers are below their normal levels.
Not: Most of rivers are below their normal levels.
We use most of before geographical names:
[from a weather forecast]
Most of England and Wales should be dry throughout the day.
Most without a noun
We can leave out the noun with most when the noun is obvious:
[talking about school lunches]
Some children brought a packed lunch but most had a cooked meal in the canteen. (most children)