To make this sound, flatly place the front of your tongue on the ridge behind your upper teeth. Some languages have a heavy L sound in which a lot of the tongue is firmly pressed. American English has a moderate L sound.
Use the video to listen and repeat common words.
black, block, blue, class, clear, close, cloud, complete, flame, floor, fly, glad, glass, glow, place, plain, plane, plant, plate, play, please, problem, sleep, slid, slide, slow.