IN THE BEGINNING I used to write 7's without any slashes or serifs, the "normal" way. I'm not sure why but I eventually started adding a vertical serif. This proved to be rather illegible and ugly, so I eventually started just writing 7's with the slash in the middle. It's become a habit that's hard to shake, though I don't really know why I ever started writing them differently.
In terms of the alphabet, there was a phase when I used to write lowercase A's as they appear in most computer fonts, with the little hook on top. I eventually decided that I didn't like the way that looked, so I've since returned to the 'usual' way.
Also, most people only take notice of the
way I write, not the what I write. It seems that I hold my pencil in a "bad" grip, with the thumb kind of pushing against my pointer finger's knuckle/nail. My dad in partiuclar enjoys telling me that my grip is terrible, but I can't really write the 'proper' way. It just looks ugly.
Jam it back in, in the dark.