My Doktovater said that in his intro phonology class they read all of phonology the first semester, and started writing theory papers the second semester. I read most of phonology over the first year and a half of student life, then started writing those papers. I tried to teach my first grad students at least a summary of all of phonology over the course of a PhD program, and found that that meant eliminating anything older than 1969 (i.e. SPE and before). Nowadays, you cannot even hope to cover the OT literature on assimilation. The moral of the story is, you have to gain both depth and breadth, and when the field approaches the infinite in both directions, something has to give.
Obviously, reading an intro textbook could be a good idea, if you get the right intro. By analogy, suppose, as a linguist, I wanted to learn some statistics, then I might ask "what's a good intro stats textbook", and my interlocutor would tell me something that is really not useful to me. That's because my interlocutor is a sociologist, and I'm not into that kind of stuff. My interlocutor should have pointed me to a textbook that makes sense in terms of my interests (e.g. "do these vowels have the same formant values?").
Why do you want to know anything about linguistics? Comparative Indo-European was the hook for me; some people approach it from the perspective of philosophy and logic, etc. To the extent that you can articulate what aspect of language and linguistics interests you, some textbooks might be better than others.
Suppose for instance that you are fascinated by the idea that there are simple mental rules that apply to abstract stored representations and result in actual pronunciations; and if you combine A+B you may get a different result than if you combine A+D or Z+A. You might also be supremely bored by the fact that in such-and-such culture, it is considered to be a sign of refinement to speak with a high-pitched voice. That would tell you that you're interested in phonology, and not sociolinguistics. Reading a sociolinguistics-heavy textbook would be counterproductive.
In the old days, self-study of linguistics could sometimes yield a good output (there was a Transylvanian linguist who did it in the 60's, forgot his name), and more often yields craziness. The problem is that in the old days, there was little or no way to externally (in)validate your craziness. Nowadays, however, the interwebs
might be useful. Let's say you decide that you want to discover the system of phonological rules for Moroccan Arabic. You make up some crazy idea like "I'm gonna listen to Youtube videos that mention Morocco". You could try assailing your own theory to see why that would be ill-spent effort, and if you come up with nothing bad, you could Ask The Internet. Caution: there are a lot of nuts out there on the internet. But I imagine Daniel would be happy to explain why that would not be the best plan

in case you had such a thought.
I am suggesting that you start with some fact about the real world, which is your primary interest, and your secondary interest is "how does one account for that fact". Political theories of language sociology have virtually nothing to say about Moroccan Arabic phonology, but potentially a lot to say about the use of Arabic in Morocco.