Happy World Digital Preservation Day 2018
Rather than spend time writing about hardcore digital preservation, which others have done much more elegantly than I could, I'd like to give some simple advice to help retain your digital documents.
Back it up
Things go wrong. Electronics fail. It's easy to overlook the process of backing up your digital files until it's too late. If this post only helps one person remember to backup their phone or computer I'll consider it a success. Do it. You can back up an iPhone to iCloud from Settings. You can backup a Mac to an external hard drive via Time Machine - in your system preferences. These days you can backup just about any digital media, the issue is usually whether you remember to or not.
Delete, deaccession, destroy. Yep, part of preservation is about destruction, or curation. There's no point in saving everything, some things don't warrant long term preservation. Over 1,000 images from a hiking trip? How many of those would be useful or relevant in 10 years? My guess is around 10. Occasionally weed out or declutter your files - you might be amazed at how much space you save and it will also save you time in the long run.
File organization is an enormous topic and isn't a one-size-fits-all situation, which makes it hard for me to recommend anything except organization itself. If you're starting with files everywhere and no idea how to organize them I'd recommend making some mind-maps first. Start with a few very large, broad topics and develop sub-topics. I'd recommend going through several iterations until you have a tree that makes sense for your needs. If you're still struggling I'd recommend looking into David Allen's Getting Things Done technique (GTD).
Once organized you might want to think about renaming files and/or folders. Name Changer is a simple application for OS X 10.7+ that allows you to batch rename files. Instead of a folder full of IMG557392.jpg you can rename files to something more significant and searchable.
Back it up
Once everything is organized (good luck with that) you should back it up, in more than one place. Make copies of your archive and store them separately.
for more info on World Digital Preservation Day:
Digital Preservation Coalition's blog posts