The "sa" in Japanese is pronounced as "sah". Try writing the katakana kana of it.
How to Write Sa in Katakana
Write the first stroke. Draw a horizontal line, going from left to right.
Write the second stroke. Near the left side of the first stroke, draw a short vertical line, going from up to down.
Write the final stroke. Near the right side of the first stroke, draw another vertical line, going from up to down. Curve it to the left to finish.
Practice writing it. Use blank kana practice sheets and go across the sheet.