Hi,
the /s/ sound in made at what we call your alveolar ridge. That is, the bumpy surface right behind your front teeth. Another way to think of you alveolar ridge is the imagine the place that you would burn if you ate pizza that was TOO hot! Put your tongue right at that spot, and you will have it in the right place to say /s/.
I apologize if this is advertising - but we have a video on our FREE software showing how to pronounce /s/ (and other sounds too) - it may help you to see that. You can get it for free at
Accent School - AccentSchool FREE pronunciation software.
Take care and please contact me if I can help you more!
Thanks,
Rebecca Allen, B.A., M.A.
founder of accentschool.com