That you've gotten this far as a freelancer means you're able to complete projects and interact with customers. I would argue those skills alone make you a seni

That you've gotten this far as a freelancer means you're able to complete projects and interact with customers. I would argue those skills alone make you a senior engineer. Over the last couple years I've transitioned from thinking of code as "hacky" versus "elegant" to thinking more in terms of maintainability. First the code has to work, but then I have to be able to understand it when I inevitably come back to fix it in a year. Toward that end I will second the recommendations below for "Code Complete" and add "Working Effectively with Legacy Code". These two books transformed my views on what makes good code.