Pretty easy (results in days): Answering questions on Quora was a relatively easy, quick win. I answered a question on salary negotiation or job interviews every day for a month, and immediately saw a lot more interest in my site.
Harder (results in 90+ days): A focus on SEO has really paid off. SEO takes a while to build up, but once it's built up, it's pretty reliable traffic source. That means I can spend time working to offer more value to visitors so they'll stick around and come back later.
It seems like you're just asking about the SEO side (not Quora), so I'll focus on that.
My book is about salary negotiation, so most of my focus is on variations around "salary negotiation". That's a pretty competitive search term, so I focus on more long tail terms like "salary negotiation email", "salary increase letter sample" and "current salary interview question".
The tools I use are all free: Google analytics, Google search console, Google keyword planner, MozBar, and Google itself.
When I want to write a new article - I have a topic in mind - one of the first things I do is hop into the Keyword planner and figure out what people are ACTUALLY searching for around that topic. Most of the time, the way _I_ describe the topic is not the same as what people are searching for.
Once I know what people are searching for, I write the same article I would've written, but I try to use the more common terms rather than my own made-up terms. (For example, I would not usually say "salary negotiation email sample" - I would say "counter offer email template" or something like that. But when people want that email template, they search for "salary negotiation email", so that's the terminology I used for that article on my site.)
I gave a very, very brief overview of some other tactics I use in a talk at this year's MicroConf in Las Vegas. Here are my slides, a link to a video, and links to some of the tools I use: http://www.joshdoody.com/microconf
I highly recommend Quora as a marketing channel. It's worth exploring for your subject. Some areas aren't great, but some are very good. Mine (interviewing, salary negotiations) is particularly good on Quora because people have LOTS of questions about those things.
You could just search for a few terms in your area of expertise and see what comes up. You'll know pretty quickly if there are a lot of questions about it, or if Quora might not work for you.
Pretty easy (results in days): Answering questions on Quora was a relatively easy, quick win. I answered a question on salary negotiation or job interviews every day for a month, and immediately saw a lot more interest in my site.
Harder (results in 90+ days): A focus on SEO has really paid off. SEO takes a while to build up, but once it's built up, it's pretty reliable traffic source. That means I can spend time working to offer more value to visitors so they'll stick around and come back later.