Part of the problem is that that you will have to quickly move your tongue for those two sounds, from the top of your mouth to between your teeth.
Perhaps this site will help you. You will want to look at two different sounds - the /l/ phoneme (found under 'liquid' tab), and the /z/ phoneme (found under the 'fricative' tab). Click on both the animated cutaway view in the middle of the page, as well as the frontal view of the mouth over on the right side.
Note these are phonetic symbols, not the actual letters of the alphabet. The 's' in 'falls' is pronounced like the letter 'z', so look for the phonetic symbol /z/.
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