Touch the tip of your tongue to the roof of your mouth just behind your teeth. Add vocal cord vibration as you release.

Americans pronounce deserve as duh-ZURV (/dəˈzɜrv/). Stress falls on the second syllable — keep everything else short and quick. You'll hear it in sentences like "He raised some valid points that deserve further consideration".
Record yourself saying "deserve" 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.
Same position as S, but add vocal cord vibration. Feel the buzz.

Flare your lips and push them away from the face. Lift the middle of your tongue toward the roof of the mouth.

Lift your bottom lip so its inner edge (where the wet part meets the dry part) touches the very bottom of your top front teeth. Add vocal cord vibration as you blow air through.

The textbook way isn't wrong — it's just not how anyone actually says it.
Stress falls on the second syllable, not the others. Stretch ZURV — 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.
Americans use a relaxed retroflex R — the tongue curls back rather than rolling. The R is one continuous sound with the vowel before it, not two separate sounds.