I've been working with a little guy on his /s/ sound which sounds more like /sh/. He wants to protrude his tongue and tends to keep it flatter than optimal. We've discussed the difference between both positioning and sound of /s/ and /sh/, and we discuss "make your sound skinnier." He's beginning to get the hang of it!
I had another little guy who was working on /s/ clusters earlier in the year. I had created some "sliding worksheets" that really seemed to help drive home the need for a strong /s/ sound before finishing the word. I thought something similar might help my sh/s guy visualize the sound better, so I created minimal pair sheets with the sliding line thinner or wider depending on whether or not it was a /sh/ or /s/.
If you'd like to give this a try yourself grab a FREE copy of shine/sign here.
If you think you'll need more practice than that, try the entire pack of eight (8) worksheets here. (Note: shine/sign is not duplicated in the pack)