Most adverbs end with the suffix -ly. This isn't true for every adverb, but the majority of adverbs end with those two letters.
Adjectives usually come before nouns and adverbs usually come before verbs. There are exceptions, but if you're trying to determine whether a word is an adverb or adjective, it sometimes helps to look at the word following it.
Adjectives modify nouns and pronouns and adverbs modify verbs, adjectives and other adverbs. If you're deciding whether a word is an adverb or adjective, find the word it modifies and determine its part of speech. After you've made that decision, you can easily figure out whether the word is an adjective or adverb.
Adjectives answer the questions, "What kind?" "Which one?" and "How many?" Adverbs usually answer the questions, "How?" "Where?" or "When?" After you determine which question the word you are attempting to classify answers, decide whether it's an adverb or adjective.