I don't have a rhyme for remembering how to write the letters of the whole alphabet, but most kids don't need it. But some letters, like b and d and p and q are tricky. Usually if my early readers come to a letter and they don't remember what it is, we just pause on that letter and sing the alphabet song while tapping on the letter until we get to the right one. They get to the point where they can do it themselves when they get stuck, and stop when they recognize the correct letter.
It is hard for the little ones to remember which of those four letters face which way, so I did come up with a little mnemonic device to help with remembering b and d:
You have to look at the alphabet in a line to understand this:
a b c d e
b is for baby
and c is for cookie
and d is for daddy.
The baby and the daddy are sharing the cookie,
and daddy has taken a big bite!
I mean, it's not like a poem or anything, so if you just explain it however you think conveys the idea most clearly to your child.
Any of you moms have little tricks and tools to share? Please do!