Press your tongue tip firmly on the ridge behind your top teeth.
Switch your voice on and let the sound flow around the sides of your tongue.
Hold "lll" with the tip still touching, then say: leg, bell, lily.
✅ Check
Say "lll" and freeze. Can you feel your tongue tip pressed on the ridge? Now check the pair: "lice" needs the touch, "rice" needs no touch at all.
⚠️ Common trap
Do not let the tip float. If your tongue does not actually touch the ridge, /l/ drifts toward /r/ or a vowel, and "lice" starts sounding like "rice". Touch is the whole point of /l/.