Be Mindful of Your Intensifiers
English has a category of adverbs called “intensifiers.” When attached to an adjective, most of them make the meaning of the adjective more intense (hence their name). Here is a short list: very, really, rather and quite. There are others, which fit into the traditional adverb role, but function as intensifiers nonetheless: Examples: overwhelmingly, unusually, uncommonly.
A few intensifiers might seem to be misnomers because they take away impact from the adjective instead of adding to it: Examples: pretty, fairly, a little, a bit, somewhat.
The sandwich looks delicious.
Now repeat the sentence to yourself six times, each time adding one of the following intensifiers to “delicious”: very, really, rather, quite, fairly, pretty. Ask yourself which one gave the warmest endorsement, and which sentences seemed tepid.
Some Tips
In general: When writing, avoid intensifiers if possible. Try to think of an adverb that more precisely communicates the trait in question. Intensifiers are, by their nature, vague. Good writing is the opposite of vague; it is precise.
Awfully, Terribly & Frightfully: These words used to mean something related to “awful” (scary in the sense of causing awe) and “terrible” (causing fright). “Frightfully” is used as an intensifier, too, mainly in British English. (Example: “Frightfully kind of you to come.”) Try not to use them in phrases that involve things we like; reserve them (if at all) for things we do not want to praise.
“Pretty” started out as slang and has hung around American English for centuries. Even so, it is still considered very informal, and is best avoided in formal writing. After all, it means “attractive in a delicate way,” something short of “beautiful.” As an intensifier, it is ambiguous: some use it to be a synonym of “very,” while others use it to mean “not very.” It has come to mean “moderately.”

“Quite” means “completely,” even though many speakers use it to mean “very.” Thus, phrases like “quite so” and “quite lost” mean “completely true” and “completely disoriented.” Do not use it with adjectives that have no gradations of meaning, like “unique” or “dead.” “Quite dead” is nonsensical.
“Fairly” is a lukewarm intensifier. In olden times, “fair” meant “good looking, pleasant,” as in a fair-haired child or fair weather. But nowadays, like “pretty,” it has fallen into the middle between good and bad. For example, a “fair grade” is a “C”, not an “A” or a “B.” “Fair-to-middling” means of moderate or medium size, strength or quality.
“Really” has a common heritage with “very.” (Both started out as words meaning “in truth.”) Children often use it repeatedly, as in “really, really, really cold.” Yes, it is a useful intensifier, and one of the strongest ones; still, in all, if you use instead a solid and precise adverb, your writing and speaking would have greater impact and be easier to understand.

“Somewhat,” “a little,” and “a bit” dilute the meaning of the adjective to which they are attached. So does “rather,” except that sometimes it can mean “very” instead. Often, one of these intensifiers is employed for irony or understatement. For example, “He was rather drunk.” We can not tell if this means “a little” drunk or “very” drunk. You need to size up the speaker and the context to find your way here. The British use “rather” much more in the sense of “very” than do we Americans.