Ok! Well some that come to mind are (a) short variable names; (b) not bothering to encapsulate state or lock things down into modules; and (c) tables for layout.
I don't do these things because they're 'rookie mistakes', of course, just like I don't order whipped cream for dessert but might like it as an extra. I enjoy the feeling of lightness that comes with naively doing what's easy, as opposed to the weight of preconceptions that in practice impede the work.
