Intonation is the rhythm of speech. Rhythm is based on stress. Because American English pronunciation was standardized in order to to be useful in mass media and global business, we stress words that represent important information. Important information often goes in this order:

1. Nouns

2. Verbs (especially near pronouns, which means the nouns are understood)

3. Adjectives/Adverbs

Of course, there can be many exceptions in different situations. For instance, maybe time is most important to you--you may stress the adverb instead of the noun.

Overall, when practicing pronunciation or preparing to speak publically, choose about two-four words per sentence that are most important to the meaning of what you need to say. Stress those words and then also de-stress the others.