Teach 'o' before 'a', 'd', 'g', 'q' because all of those letters begin with the same circle. Mastery of 'o' is mastery of half the alphabet's lowercase shapes. Always trace 'o' counter clockwise, starting at the top. This is the standard direction that makes joining letters in cursive easier later. If your child draws clockwise circles, gently correct early. The habit is hard to undo.

A circle is a promise that comes back to itself. Draw 'o' well, and you have already drawn the bones of a, d, g, q.