"What skills do self-taught programmers commonly lack?" is a very different question from "What skills do self-taught programmers need to learn?" What you need

"What skills do self-taught programmers commonly lack?" is a very different question from "What skills do self-taught programmers need to learn?" What you need to learn depends a lot on what you plan to do. Programming is a large field with lots of different specializations. If all you want to do is make web apps and mobile apps, there is probably no need to learn how to write an OS, you only need to understand how the various OSs differ from one another. On the other hand, if your passion is in systems programming, there is probably no need to learn about the latest CSS preprocessor. All of these things are good to know, but one person cannot, and does not need to, know everything. Pick one or more specializations that you're particularly interested in, and learn a lot about them. Don't completely ignore all the other fields, but satisfy yourself with a high-level understanding of (1) what those fields are generally about, (2) why they're important, and (3) when you should defer to the judgment of someone who is an expert in one of those fields. Anyway, here's one specific suggestion that I don't think anyone has made yet: if you do anything web-related, learn what the various protocols that make the internet tick (http, smtp, dns, etc.) actually work under the hood. You should be able to create a text file, pipe its contents to a telnet session, have the machine on the other side return useful information, and be able to parse the result. Not because such a skill will get you a job, but because the insight you gain during the process will put you ahead of the majority of "web developers" who have no idea how much complexity Rails hides behind its ass. When you're done with text-based protocols, move on to binary protocols. (Memcached is good for practice because it uses both.) Incidentally, this will also teach you a lot about commonly used data structures.