There are already some great answers, but here is my two cents.

> What did you do to become fluent in another language?

For me the short answer was I took classes for the beginner levels, and actively looked for opportunities to use the language. After the beginner stages I self studied, with the help of iTalki teachers, tutors, and friends that spoke my L2.

The long answer is:
1) I took courses that taught me the fundamentals. By that I mean all the sounds a language can produce, and the basics of it's writing system.
2) The course covered reading, writing, speaking, and listening. Each one reinforced the others, along with frequent testing.
3) I spent a minimum of 2 hours a day 5 days a week practicing, reviewing, and learning, my first year learning the language.
4) Once I was at an A2/B1 level, I took a 4 week intensive summer course in my L2's country. During that time I transitioned from learning about my L2 with English to talking about it and learning it using only the L2.
5) I would constantly put my self into real world situations that forced me to use my L2. For example, as a beginner one thing I did was go to a local L2 restaurant. I tried to order in my L2, and tried to understand what some of the patrons were saying. I also went to conversation exchanges, and culture meetups. There are many things you can do.
6) I didn't limit myself to what the course taught, and actively searched for things that interested me, like dubbed versions of movies I liked, or vocabulary related to my hobbies.
7) Do things that keep you motivated. For me this was reading positive blogs from people like Benny Lewis, or scheduling milestones.

I could go on and on, about specifics, like memorization techniques, or the importance of speaking as early and as often as possible, but there are tons of articles on the web about that stuff, and any language learner that looks outside their course will find them.

> How long did it take you?

There is no one size fits all answer for this. Depending on how different your target language is from your native language, and what you have defined fluent as this number can be all over the place.

Also, I find that with each language I learn, the next one becomes easier to learn. For example after learning 50 Mandarin works a week as a beginner, learning 50 Spanish works a week seemed like a cake walk, especially with all the cognates. Another example is I am learning Japanese now, and learning Kanji is a cake walk for me. First because I already learned to write characters in Mandarin, and second because most kanji that I have seen have the same or similar meaning as their Chinese counter part.

For me personally learning Mandarin. I was conversational at a very basic level after a little over a year. After two years I was comfortable with day to day conversations. Where I am at now after three years is that I can keep up with group conversations and even participate, but not yet at the same level as English.

Also, the learning is never done. There comes a point where learning becomes more passive, you pick up words naturally from a conversation or you just review a bit every once in a while, but that usually only applies to people who end up speaking their L2 all the time. Like someone who has moved to their target languages country. The rest of us still need to set aside time for practice and study, or the skill will rust.

> It seemed like you were implying a question with your first statement of being overwhelmed with choice.

Pick one and stick to it. I would suggest you find a book, software, or course, that covers reading, writing(not typing), listening and speaking. If it doesn't cover one of these and you are willing to supplement it, that's fine. Otherwise find another option. When you are deciding skim it and make sure you won't get too bored with it.