Drop your jaw moderately. Touch the tongue tip behind the bottom front teeth and lift the mid-front part slightly toward the roof.

Americans pronounce emphasizes as EHM-fuh-sahy-zuhz (/ˈɛmfəˌsaɪzəz/). Stress falls on the first syllable — keep everything else short and quick. You'll hear it in sentences like "The coach emphasizes the importance of teamwork and communication".
Record yourself saying "emphasizes" and play it back. The mic stays on your device — nothing's uploaded.
4 syllables, 9 sounds. Tap a syllable to jump to its row, then explore each sound's mouth shape and how it's made.
The textbook way isn't wrong — it's just not how anyone actually says it.
Stress falls on the first syllable, not the others. Stretch EHM — keep everything else short and quick.
Don't pronounce the first syllable too fully. The unstressed syllable reduces to a schwa — the lazy "uh" sound — in casual speech.