Development Job

I’ve been doing web development for a few years now just doing personal stuff. I’d like to consider doing some paid development either in spare time or do it full time. What is the most important stuff to be well versed in? I’m currently working in PHP with MySQL. I can do ASP with Access/MSSQL, but I hate it. For all of you PHP developers that have full time jobs, what is the most important to know? This applies for individuals or people that work in groups. Thanks

System integration is probably the best thing you could learn. APIs XML Soap Curl ect.. Oh and proper DB design is unfortunately a rarity with alot of ‘developers’