Raise the back of your tongue to touch the soft palate. Add vocal cord vibration, then release.

Americans pronounce gloomy as GLOO-mee (/ˈglumi/). Stress falls on the first syllable — keep everything else short and quick. You'll hear it in sentences like "The overcast sky made the day feel gloomy and dark".
Record yourself saying "gloomy" 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.
Raise the back of your tongue to touch the soft palate. Add vocal cord vibration, then release.

Place the tip of your tongue against the alveolar ridge just behind your top front teeth, the same contact point as /t/, /d/, and /n/. The difference is what happens to the air: for /l/, you let it flow continuously around the <em>sides</em> of the tongue (that's why /l/ is called a lateral). Turn your voice on the whole time. Lips stay relaxed, no rounding or flaring. For the Dark L variant at the end of a syllable, also pull the back of the tongue up and back toward the soft palate.

Round your lips into a tight circle. Let your tongue rest in the middle of your mouth, slightly raised.
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 GLOO — keep everything else short and quick.