What should every programmer know about web development?
I went to school for a BSE in Computer Science. I gained a good understanding of the foundations and principles of CS, how to make intelligent choices in design, as well as a handful of other invaluable things relating to the field. Unfortunately, there we no courses in the area of Web Development, which is nonetheless the path I chose to pursue.
Most of my Web-related skills are self taught: PHP, MySQL, HTML, CSS, JS, and other trace elements. I now have roughly one year of professional experience, but I work at a young startup where the senior developer is 23 years old, just like myself.
Without the benefit of an early start (as it seems many other SO developers have had), or an experienced developer to act as a mentor, what are the best things I can do to 'catch up' (and hopefully excel)? Is my time better spent focusing on refining my proficiency as a PHP programmer or should I consider exploring Ruby, ASP.NET, and Java (all of which I have little to no experience with) to round out my skills? Should I jump into coding with CakePHP, CodeIgniter, or [insert framework here], or should I be building things myself (I have noticed that jQuery enables a certain ineptitude with JS)?
I guess more simply, what have you found to be the most beneficial to your career on the web?