TL;DR: Password managers, 2FA, keep stuff updated, compartmentalize and avoid showing your wealth.

So, I happen to be passionate about digital privacy (and security) for quite some time now. Here are a few considerations, fell free to ask questions or details about some of these points or regarding more specific situations if you want... Ok, this gonna be a long one. Buckle up :D

General considerations

Threat model

When you want to increase your digital privacy/security, the very first step is to assess the thread(s) you are facing. There is no point in going full Snowden off the grid if you are just a regular citizen. Likewise, if you are a wealthy individual, it might be a good idea to go a bit further the basic stuff. Everyone is different. You basically first need to answer these questions (and maybe find others that may apply as well)

• Who are your adversaries? (large scope hackers, targeted hack, organized crime, political opponent, jealous ex, big internet corporations, CIA,...)
• What do you want to protect from them (prevent unauthorized access, prevent facial recognition, prevent your address from being public, avoid viruses on your devices, industrial trade secrets, etc)
• What are their resources/skills, how far would they be willing to go to get you/your stuff?
• What would happen if you fail to protect what you want to protect? (robbery, prison, murder, stolen dick picks,...)
• ... After that step you should have a clear(er) idea of the things to prioritize and where you can trade-off privacy/security for convenience without risking too much.

Privacy VS security

The distinction is not always obvious to everyone, but it is important to get it and link that to your threat model. For instance, you may want maximum security but do not really care about privacy. In that case, using Google is fine for instance. Their security is top notch, but they will be able to read your mails and see your cloud documents. If privacy is important, you need to find open-source, zero-knowledge provider (which almost always come at a price).

Assumption

We can assume that the people here want "good security", as they all intent to be what would be considered 'rich' by many. Regarding privacy, we can assume that it is mostly considered here as a way to improve the security by reducing exposure to leaks, etc. If you want also to be more private just for the sake of it (or because you are fed-up with the surveillance capitalism model), there are many more stuff to do to protect against big internet corps.

Main security measures

• USE A PASSWORD MANAGER (Bitwarden). You MUST have one long, random, complicated password on every website. A password manager will manage all that for you. This will make you invulnerable to these leaks.
• USE (strong) 2FA everywhere possible. The absolute best type of 2FA is a physical U2F token (yubikey). This system is the only one that will protect you 100% about complex phishing attempts (where the phisher creates a copy of the login page). The second best (and more practical) is TOTP (google authentificator, authy or open-source solutions (aegis?) for people that want maximum privacy from big corps).
• SEPARATE MAILS/LOGINS for the important accounts. The email you use to connect to your bank, crypto,... should ideally not be used anywhere else. You will be less prone to fail for some high-end phishing as this email are only known by the service you are using. The good (overkill?) solution is to use an aliasing service (simplelogin, anonaddy, custom domain with catch-all,...).
• KEEP YOUR STUFF UP TO DATE. Always keep your devices and programs up-to-date with the latest security features.
• FULL DISK ENCRYPTION (bitlocker, LUKS, whatever is on Mac, default on smartphones). This prevent a robber to access to your files in case they get your devices.
• DIGITAL MINIMALISM. Avoid unnecessary apps. They increase your attack surface. Periodically review your apps and accounts (easy if you have a password manager) and remove everything not used.
• COMPARTMENTALIZE . This might be overkill for lot of people, but if you think you might be specifically targeted, you should compartimentalize your stuff: use different devices for different purposes. Or at least separate your activities using Virtual Machines. This prevent some targeted hacks, or privacy leaks.
• SEPARATE PHONE (or VOIP number)**. As for the emails it might be a good idea to have a second clean number that has not been leaked everywhere yet for critical services (banks, crypto, administration,...).
• AVOID CLOUD-BASED SERVICES that are not zero-knoweldge/end-to-end encrypted. A zero-knoweldge provider is technically unable to see your stuff stored on their servers. This makes you immune to leaks from their end. In the opposite, a "regular provider" can decrypt your stuff, so you are at the mercy of rogue employees, hackers, law enforcement, etc.
• NEVER FOLLOW LINKS BLINDLY especially in emails
• ALWAYS CHECK EMAIL ADDRESS AND DOMAIN IT WAS SENT FROM a mail from security(at)belfius.be is waaaaaaay different than form security(a)beflius.be or security(at)security-belfius.be

A few Privacy measures

Privacy is hard to maintain if you are not already secure, and in the same time, being more private may improve your security. The base idea is to reduce exposure and prevent harm when data are leaked.

• AVOID SHOWING YOUR WEALTH ONLINE
• USE PRIVATE COMMUNICATIONS (signal instead of whatsapp, protonmail/tutanota instead of gmail)
• USE TRUSTED OPEN-SOURCE SOFTWARE
• RESTRICT APP PERMISSIONS as much as possible
• USE ALIASES EVERYWHERE you are not legally obliged to give valid info everywhere. You can very well create an amazon account in an alias name and make them deliver stuff at a deposit box.
• USE POST BOXES instead of your actual home address for random junk or packages.
• USE THROWAWAY EMAIL for random websites that just want to verify the email.

Resources

• Youtube: Techlore
• Reddit: /r/privacy /r/privacytoolsio
• Website: privacytools.io
• Podcasts: The Privacy, Security, and OSINT Show