If there's one thing about the leg to remember it's that it's a pain
But really learn about the three major muscles of the foward-facing thigh: the vastus lateralis, vastus medialis, and the rectus femoris
The first two form "teardrops" and overhang the knee, the outer inserting slightly higher than the inner, and the last is a triangular wedge between the two
There's much more nuance to the leg aside from those shapes but it's a great jumping off point to nail down the main idea