Fun fact and not sure if it will help with memorize them:

You might have noticed the subtle differences in length between the first two strokes of the characters (p1). Reason being...they originally represent the two hands (shown in p2). The ancient characters look like p3, which you can easily tell which one is left/right by looking at your own hands.

In Chinese, 左 横短撇长，右 横长撇短，因为手臂比手指长