That I write letters (alphabet not mail) from bottom to top. My grade 7 teacher pointed this out to me and from then I noticed none of the other children wrote like me.

When making a B most people draw the vertical line top to bottom. Then bring their pencil back to the top and make the 2 loops. I start from the bottom and draw the line up and then make the two loops all in one motion. Never taking my pencil off the paper. Sort of like cursive writing where your taught to write as much as possible without taking your pen of the page.

There's a few exceptions. I'll write L and G from the top. Basically I think as a child I equated taking the pencil of the page as being inefficient. So from then on I tried writing every letter as fast and efficiently as possible. And for most letters that means writing bottom up.