I’m always hesitant to tout web development as a skill (specifically front-end), because everyone interprets that differently. To some, it means basic HTML and CSS, but some consider it to be complete js and php knowledge.
So, instead of leaving it up to guessing, I’ll layout all of the coding languages I regularly use.
I use only the most up-to-date and semantic HTML5 markup. I do provide fallbacks in my stylesheets and scripts if your main clientele is using IE 8 or below, even if it kills a little bit of my soul.
I work with both of the main preprocessors, Sass and LESS, to streamline my stylesheets and save a ton of time. This provides you with many of the Webkit, Mozilla, etc., prefixes that may be needed to support your site.
I’ve developed for both WordPress and ExpressionEngine (huge preference for WP, which this site is), so I know enough PHP to get me in trouble. It’s essential for building a website that’s easily editable, so hey, I learned it.
Once I was introduced to version control (and stopped accidentally deleting files from it), I won’t do a site without it. Using git has streamlined my development process by shocking leaps and bounds.