How to correctly pronounce the letter 'S' in English?

Try pushing your tongue back a little bit. Not a lot, but take a moment and read this very carefully. Feel the tip of your tongue? Not feel it with your finger, but can you feel it? Okay, place the tip inside your teeth toward the top, where the teeth come from the gum, not the edges. Don't keep it there, but use it as a reference to how far your tongue should go. Move it down a little so it's slightly raised. Don't shut your teeth completely, but open them so you can fit a fingernail inside. Then just try making the 's' sound with your tongue in this position. I wish I was there to help you, because then it would be so much easier. Have someone there to help you.