Press your tongue tip against the ridge behind your top teeth.
Switch your voice on and hum through your nose: "nnn".
Hold it for two seconds, then say: no, sun, ten.
✅ Check
Hum "nnn" and pinch your nose. The sound should stop. Then say "sin" and "sing" and feel the difference: tip at the front for "sin", back of the tongue up for "sing".
⚠️ Common trap
Do not confuse it with /ng/. For /n/ the tongue TIP touches the front ridge. If the back of your tongue rises instead, "sin" turns into "sing".
Practice: /n/
Words
nonˈoʊ
sunsˈʌn
tentˈɛn
nightnˈaɪt
dinnerdˈɪnəɹ
Sentences
No, thetrain leaves atnine.nˈoʊ, ðə tɹˈeɪn lˈivz æt nˈaɪn.
We haddinner atnoononSunday.wˌi hæd dˈɪnəɹ æt nˈun ˌɔn sˈʌndˌeɪ.