Adjectives are words that modify nouns or pronouns by defining, describing, limiting, or qualifying those nouns or pronouns.

Adverbs are words that modify verbs, adjectives, or other adverbs and that express such ideas as time, place, manner, cause, and degree.

Use adjectives as subject complements with linking verbs; use adverbs with action verbs.
Examples:

• The old man's speech was eloquent. (ADJ)
• Mr. Potter speaks eloquently. (ADV)
• Please be careful. (ADJ)
• Drive carefully. (ADV)

GOOD AND WELL

Good is an adjective; its use as an adverb is colloquial or nonstandard.
Correct:

• He looks good to be an octogenarian.
• The quiche tastes very good.
• He gets along well with his co-workers.

Colloquial:

• He gets along good with his co-workers.

Well may be either an adverb or an adjective. As an adjective, well means "in good health."
Correct:

• He plays well. (Well is an adverb.)
• My mother is not well. (Well is an adjective.)

BAD OR BADLY

Bad is an adjective used after sense verbs such as look, smell, taste, feel, or sound or after linking verbs (is, am, are, was, were, and other forms of be).
Example:

• I feel bad about the delay.

Badly is an adverb used after all other verbs.
Example:

• It doesn't hurt so badly now.

REAL OR REALLY

Real is an adjective meaning "genuine"; its use as an adverb is colloquial or nonstandard.
Nonstandard:

• He writes real well.
• Have a real nice day.
• The company is real pleased with your work.

Correct:

• This purse is real leather. (ADJ)

Really is an adverb.
Examples:

• He writes really well.
• Have a really nice day.
• The company is very/really pleased with your work.

NOTE: Really has become an overworked adverb; therefore, one should use alternatives such as very or exceedingly whenever possible or leave out the adverb entirely.

SORT OF AND KIND OF

Sort of and kind of are often misused in written English by writers who actually mean rather or somewhat.
Incorrect:

• Lannie was kind of saddened by the results of the test.

Correct:

• Lannie was somewhat saddened by the results of the test.