Give students a transparent tool to help them label triangles!
Students often have trouble labeling parts (such as x, 2x, a, b, c, opposite, adjacent, hypotenuse, etc) of triangles for Special Triangles, Pythagorean Theorem, and Trigonometry. To help my students do this correctly, I give each student a labeled triangle printed on transparency film.
Then when students are working on one of these types of problems, they line up their transparency with the problem on their paper. They line up