There are a number of blogs that I follow dedicated to the Salesforce ecosystem. Not every one of these is code-focused, but they've all taught me a number of things. In no particular order, here are a few to get you started:
http://www.codefriar.com—OK, shameless plug here; this one is my blog. I mostly talk about Salesforce and mobile development.
http://www.adminhero.com/—Brent Downey spends his blog time helping readers understand how to get the most out of your Salesforce org. While Brent doesn't do much with code, his blog is invaluable when it comes to mastering the declarative aspects of the Salesforce ecosystem.
http://andyinthecloud.com/—Andrew Fawcett's blog is the gold standard for code-based Salesforce blogs. He's responsible for building a number of free packages like the Declarative Lookup Rollup Summary tool, and the UML chart generation tool I mentioned in the team development chapter. His articles are easy-to-read and packed full of useful information.
https://www.buttonclickadmin.com/—Whereas Andrew's blog is the gold standard for coding blogs, Mike Gerholdt is the venerable gold standard for declarative development blogs.
Podcasts are a great way to learn while you are driving to work, or otherwise occupied by a mind-numbingly boring task. There're only a couple I want to highlight here, but they're well worth your time:
https://itunes.apple.com/us/podcast/code-coverage-salesforce-developer/id880831007?mt=2—Code Coverage is led by two of the smartest and most experienced developers I've ever met. Matt Lacey and Steven Herod spend their podcast time interviewing various people in the Salesforce ecosystem on a wide range of topics. Want to learn more about Trailhead, for example? Check out Episode 21.
http://thewizardnews.com/wizardcast_home/—Just as informative, but with a lighter-hearted tone, is the WizardCast. Led by two characters known as SalesforceWizard (complete with wizard hat!) and SalesforceYoda, these two will make you laugh, even as you learn all about using flows.
First, do not pass go, and do not collect $200—go here: https://developer.salesforce.com/trailhead, sign up, and start working though trails. It doesn't matter what your experience with Salesforce development is, go work through Trailhead. If nothing else, it's a great way to highlight your skills on your LinkedIn page! Trailhead is different than other online learning systems because most of the trails require you to log in to a development org and demonstrate your skills, not just answer questions. In other words, you'll learn a skill, say how to write a bulk trigger, and then you'll have to actually build a bulk trigger! Trailhead will then execute tests against your trigger and only if it passes will you get the points and the badge.
Despite the skills you'll pick up going through Trailhead, you're inevitably going to run into an issue or quirk of the platform that you just don't quite understand. When that happens, here are a few resources you can reach out to online.
https://success.salesforce.com/—The venerable Success community is home to the largest online community for any platform I've ever discovered. Here, you can ask your questions, no matter how big, small, detailed, or just plain noobish. If you're lucky, your questions will be answered by some of the community's legends such as Steve Molis. Remember to search the archives before posting! It's likely you're not the first person with this problem, and there may already be an answer waiting for you!
Like the Success community, the Salesforce Developer forums are a great place to ask and answer questions related to Salesforce development. While you're more likely to find questions and answers about validation rules and page layouts within the Success community, you're more likely to find detailed questions about Apex collections and HTTP callouts on the Developer forums. This is a great place to get your feet wet answering questions. Do make sure, however, to use the code formatting and hyperlinking buttons to properly set up your code and links.
Code writing developers from any background are likely familiar with StackExchange. What you may not know is that there's a StackExchange specifically for Salesforce: http://salesforce.stackexchange.com/. Here, you'll find a tightly moderated question and answer site covering everything from Apex enums to Marketing Cloud AmpScript questions, along with detailed, useful answers. Note, however, that the StackExchange system does not take kindly to questions that simply ask someone else to do your work.
Remember that with any of these three question and answer sites, it's always best to present your formulas, code, or validation rules in their entirety. It's frustrating to try and help only to discover that the problem is clearly in the method you didn't share.
Lastly, there's an old means of real-time communication called Internet Relay Chat, or IRC. IRC has federated server networks that individuals connect to, and rooms that are tied to topics. The community maintains a fairly vibrant room, called #salesforce on the Freenode network. You can join us by visiting: https://webchat.freenode.net/. You'll need to supply your own nickname and prove you're human, but if you do that and specify #salesforce for the channels input, you'll soon see messages scrolling across your browser. Feel free to ask questions; we don't bite.
Thanks for reading my book! Feel free to follow me on Twitter at @codefriar.