Pretty much every notes, journal, to-do app, and writing app has a tagging system now. With it, you're supposed to be able to easily organize everything so you can find it instantly, but tags are a bit of an ambiguous idea that are hard to really use well. I did it wrong for years, but I've finally come up with a system I like.
To be clear here: I'm not talking Twitter hashtags, blog tags, or anything else tied to the internet at large. Just tags for files. Tags exist to help you find what you're looking for quickly or browse through similar items. Basically, it's a way to put digital stuff into several places at once. For example, let's say you're tracking your receipts with Evernote. You could put all your receipts in a notebook, and then tag them with something like like, "tax deductible," or "work reimbursement," or whatever else. This way, you can easily filter out similar items to find what you're looking for. Tags are great for tracking things like receipts throughout the year, but they're also handy for organizing notes at school, journal entries, and plenty more. Tags make it so you can create your own system where items are connected, curated, and sorted.
Tags have been around for a while, but I've never really latched on to using them. For years, I've just haphazardly tagged things on a whim, and subsequently, I have a mess of files, tags, and various systems that don't make any sense or organize my ideas at all. I always thought I was doing it wrong, and only recently have I realized that there isn't a wrong way to do it. Finally, tags clicked in my head, and I've started using them to actually organize my mess of ideas.
Create a System Before You Start and Stick to It
To get myself to actually use tags I needed to settle on my own system. I'm the type who needs a little bit of order, and my willy-nilly tagging methods meant I'd use too many synonyms, shift between plural and singular, and forget to tag items that needed it entirely. Now, I use tags in just a few apps: Simplenote, Day One, and Mavericks. I keep my system simple, with three basic tiers: Context, Topic, and Location. If I'm going to tag a note or file, I try to add all three.
Context: I use contexts to separate by the type of project. This is basically my first tier of organization and includes words like: Lifehacker, Fiction, Interview Prep, or Public Speaking. The goal for these tags is to provide the place where these ideas, notes, or whatever will one day end up, not micromanage by project (ie, "Lifehacker Post About Tags" or whatever). I try to use as few contexts as possible, so within something like "Public Speaking" are notes about telling a story publically and a copy of a best man speech.
Topic: If contexts are my broad stroke of organization, topics are my micromanagement. This is where I'll get a little more precise with my tagging, but still keep it broad it enough that it's applicable across several entries. For Lifehacker, I'll also add tags like, "feature," "how to," "psychology" or "tests." The main goal here is to make it so I can cross reference across contexts and see trends in what I'm writing and thinking about over time, so I'm typically pretty loose with what I'll add here, but I only bother to add a topic tag if it'll actually get used in other places.
Location: My memory is tied to location in a very extreme way. If I'm trying to remember something, I usually need to put myself back at the place where I initially thought of it. It's a little weird, but it's how my brain tends to work, so I try to use it to my advantage. For notes, ideas, and anything else where I'm jotting something down quickly, I add the location—whether that's my desk, the car, the coffee shop, or the shower, so I can use that as a means to help me remember a bit more about the initial inspiration.
Of course, I also use tags in simple, descriptive ways when applicable. I'll label a subset of items, "tax deductible" when it makes sense, but it's incredibly rare that I need to organize in that way because I don't have that kind of data to organize. The main question you need to ask yourself before setting up your system is: "What will I need to remember this for in the future?"
How you tag is really up to you, but it'll be easier if you lay down the rules for your system before you start. When I was setting mine up, I came across a few others I really like, including Science Fiction author Jamie Rubin's tagging system for writing and research, assistant professor Allan Johnson's tagging system for school notes, and Day One's suggestions for Tag Groups. I've basically taken a few bits from each of theirs and modified them to work for me.
Remember That You Don't Need to Tag Everything
Here's the thing that took me a long time realize: you don't need to tag everything you do. Some files, notes, journal entries, and to-dos don't need them. If spend your time tagging everything you'll never get anything done.
So, what can you skip tagging? That's up to you, of course, but for me it's files that I know are temporary, items that are already organized by project, journal entries that don't have a lot of purpose, or notes that have already descriptive headlines. Basically, if a tag can't be used more than once or won't connect a thought to another, I don't bother.
Everyone's system of tagging is a bit different, but if you've shrugged it off for years, or worried that you'd spend too much time catching up, it's worth a look again. While I'll probably never go through the effort of tagging old files and notes, I'll at least have some semblance of organization moving forward. Or at least as long as I stick to one piece of software.