Which letters to design first to base others off of it?

I've always wondered how this works and I've not come to a one fits all solution and every time it's me winging it with a few letters to start off and then in the midst I get stuck not knowing how to continue for certain letters incorporating the same style. I mean unusual looking letters, like ornamental wood type or something that's just different. So which letters to draw out first to use as reference to draw up the remaining glyphs? 

Thanks!