When a “s” in Spanish is followed by another consonant it is usually preceded by an “e.” As such, when an “s” is followed by a consonant in English the Spanish speaker often wants to precede with an “e” like would be usually done in Spanish. However, in English this is rarely the case (although there are some exceptions like “esteem”).
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.
Speak a line of words that includes both "S"s in Spanish that are not followed by consonants with words in English that are.
For instance: Sol sun sleep school start Santiago statue student serpiente snake
Repeat this line--or a similar sequence--many times, almost like a tongue twister. Ideally, the "s" from the Spanish words that are followed by vowels will creep in (in a good way) to the English "S"s that are followed by consonants.
Try to do this in the morning each day to set a good habit for the day in terms of your pronunciations of "S"s.