A snake makes the sounds"sssssssssssssssss". So before speaking words that begin with S followed by consonant, make the long snake sound to lead in.
1. S+/k/ score, skin
2. S+/l/slow, sleep
3. S+/m/ small, smile
4. S+/n/ snow, snail
5. S+/p/ spot, special
6. S+/t/ steak, stay
Example: Sss-teak, Sssnow, Ssspecial
Maybe you start with a long sound, like SSSSSSSSSSSSSSSSSSSSSSSSSnow. Say it many times. Over time, reduce the length of the lead in, so the process maybe look like:
SSSSSSSSSSSSSSSSSSSSSSSSSSSSSSnow
SSSSSSSSSSSSSSSSSSSSnow
SSSSSSSSSSSSnow
SSSSSSsnow
SSnow
Snow
And then you will finally be speaking like a serpiente or a "snake".
This is a slight adaptation of an idea from Katherine Garcia Molina, the principle idea and the examples 1 - 6 are directly from her.