Tech Solvency / User security advice

General

Consumer Reports Security Planner - fantastic tool, strongly recommended!
Top Ten Important Cyber Security Tips (Cisco)
Security Education Companion (EFF)
Security Tips (US-CERT)
Stop. Think. Connect (DHS)
On the Internet (FBI)
Simple Security Step-by-Step Guide (ZDNet)
The Motherboard Guide to Not Getting Hacked
Device and Account Security Checklist (Bob Lord)
Security in a Box - Digital Tools and Tactics
Protecting Yourself on Social Networks (EFF)
Getting started with security keys (Paul Stamatiou (@Stammy))
Securing Portable Electronic Devices During Travel (CISA)
Identify Theft Central (IRS)
A Comprehensive Guide on Securing Your System, Archives and Documents (Elcomsoft)
Choosing a VPN That's Right For You (EFF)
Big-Ass Data Broker Opt-Out List (Yael Graeur)
Zebra Crossing: an easy-to-use digital safety checklist (Narwhal Academy)
Amazon Cybersecurity Training - same as given internally at Amazon

Specific populations - various

Tips for Mobile Security (Kaspersky)
Practical Security for the Prudent American
Enabling HTTPS for small sites (Facebook)
Twitter thread on research in under-represented user populations (@random_walker)
Digital Inheritance - what happens to your data when you die? (SANS)
NCSC guidance for charities
13 security tips for journalists covering hate online

Specific populations - seniors

Internet Safety for Seniors (State of Washington)
Tips for Mobile Security (Kaspersky)
Practical Security for the Prudent American
Enabling HTTPS for small sites (Facebook)
Twitter thread on research in under-represented user populations (@random_walker)

Specific populations - children/teens

Keeping children safe online (US-CERT)
Safe Online Surfing - online course in cyber safety for kids and teens (FBI)
How to manage your child’s online presence (Malwarebytes)
SchoolSafety.gov - resources for cyber in K-12
Helping kids be safe, confident online explorers (Google)
How to protect your child's identity (Malwarebytes)

Specific populations - business, small business, and small governments

Protect Your Business (cyberaware.gov.uk)
PCI Small Merchant Tools and Resources
Cybersecurity for Small Business (FCC)
Safeguarding your biggest cybersecurity target: Executives (CIO.com)
Protect your small organization against electronic adversaries (Prof. Dan Wallach, Rice U)
Small Business Cyber Security Guide (Australian Cyber Security Centre (ACSC))
Cyber Essentials (CISA)
Capacity Enhancement Guides (CISA) - included guidance for protect social media accounts
NCSC guidance for business communications (SMS and telephone)

Advanced (for targeted users)

High Security Starter Pack (EFF)
Advanced Protection Program (Google) - "The Advanced Protection Program safeguards the personal Google Accounts of anyone at risk of targeted attacks – like journalists, activists, business leaders, and political campaign teams"
Extreme Security Measures for the Extra Paranoid (Wired)
Tech Solidarity resources for targeted populations
SIM Swap Scams: How To Protect Yourself (FTC)
Compromised Personal Network Indicators and Mitigations (NSA)

Two-Factor Authentication

twofactorauth.org - a list of sites supporting two-factor authentication
Universal 2nd Factor (Wikipedia) highly recommended for Google, Dropbox, Facebook, FastMail, GitHub, etc. - on Chrome, Firefox, and Windows 10 (FIDO 2.0)
U2F reviews (Brad Hill, Facebook)
Yubico Authenticator app (Android)
Unofficial U2F FAQ

Online security tips from Google (2018-06)

Use unique and strong passwords [and use a password manager to manage most of them]
Keep your software up-to-date [both mobile and desktop]
Protect your mobile devices [passcode/PIN/fingerprint; test remote locking capability; delete unused apps; review app permissions regularly]
Learn how to avoid phishing attempts [avoid clicking links in reminder/action emails - go directly to website; g.co/passwordalert; use Chrome or Google Drive to open suspicious attachments]
Protect your account with 2-Step Verification [physical U2F/FIDO2 key, Google Authenticator/Authy/Duo TOTP app; SMS]
Extra protection, for those who need it most [journalists, activists, business leaters, political teams - g.co/advancedprotection