As in most adjectives, some adverbs form their comparative degrees by adding -er and their superlative degrees by adding -est.

Example: fast, faster, fastest

Most adverbs with two or more syllables form their comparative degree by using more and their superlative degree by using most.

Example: attentively, more attentively, most attentively

Irregular adverbs change completely when in their comparative and superlative forms.

Example: badly, worse, worst

Avoid double comparison.

Example: more earlier, most earliest