Touch the tip or front edge of your tongue to the roof of your mouth behind your teeth. Air flows through your nose.

Americans pronounce nephews as NEH-fyooz (/ˈnɛfjuz/). Stress falls on the first syllable — keep everything else short and quick. You'll hear it in sentences like "He practices card tricks to entertain his nephews".
Record yourself saying "nephews" and play it back. The mic stays on your device — nothing's uploaded.
2 syllables, 5 sounds. Tap a syllable to jump to its row, then explore each sound's mouth shape and how it's made.
Lift your bottom lip to touch the very bottom of your top front teeth. Blow air through this contact point without voicing.

Start with the tongue mid-front raised high, almost touching the roof of the mouth (but not touching). Glide into a tight lip circle as the tongue back lifts.
Same position as S, but add vocal cord vibration. Feel the buzz.

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 NEH — keep everything else short and quick.