NB: this list was written a while ago in collaboration with a friend and in a rather special context. This version is slightly modified, but still contains some stylistic language and grammar. I don’t actually follow all of the advice personally, but I aspire to.
I think it is bad practice to not use a Linux distribution. I understand it can be daunting to get started, but there are many easy distributions for beginners: first choice is Ubuntu, but if you want something more similar to Windows, try Kubuntu, or ElementaryOS which is more similar to MacOS. Once you get used to that, you can try something like Arch Linux which gives you more (and very easy) control over your computer. Maybe not best security-wise, though, so be careful - maybe use Debian (or Gentoo if sperg) for best security.
You must use a phone that is not tied to Google or Apple! Android is ok, but you must use de-googled version like LineageOS or /e/OS (if you are a noob and think installing alternative android version is too hard, I recommend buying refurbished phone from /e/). If you are not a modern degenerate and have no need of spending 8+ hours per day poking at a smartphone, consider getting the upcoming PinePhone, which will be best possible phone from the perspective of security/privacy/freedom.
On desktop, you must use Freetube, or at least invidio.us in the browser. This stops Google from profiling you, and also gives better experience with no ads etc. You should use the Invidition browser plugin in order to force Youtube videos to go through an instance of invidious.
On android, you must use NewPipe, which is similar to Freetube and much much much better than the shitty bloatware tracking app that google provide.
I actually recommend Firefox, despite some problems with Mozilla being a bit evil. They are much less evil than Google, though, who in practice control the future of Chrome-derivatives like Brave. DO NOT USE CHROME. The reason I recommend Firefox is that the addons are generally better. In order to make it easier to install addons which Mozilla do not like, you can use the developer version of firefox. I strongly recommend the following addons:
Decentraleyes, partly stops you from getting pozzed by google, amazon, etc
Invidition as mentioned earlier redirects youtube requests to invidio.us, and optionally also twitter requests to nitter which is similar to invidious, but for twitter obviously. I strongly recommend this, but if you are a twitter addict, you may want to wait until it is a bit more mature and has anonymous account support like invidious.
AdNauseam is the best adblocker to truly fuck over ad delivery networks like google, I highly recommend
Facebook Container, if you use faceshit
For searching, try to avoid using Google. DuckDuckGo is the best due to its !quickbangs, but startpage is also a good Google alternative (they pay Google for the results, though).
Facebook - Frost
Youtube (and soundcloud) - NewPipe
Google drive/dropbox/similar, also calendar syncing - Nextcloud
Public transit planning: Öffi
Google keep, taking and sharing notes (e.g. shopping list for waifu): Simplenote
2-factor authentication: Aegis Authenticator
Ad-block: AdAway. You can also use the firefox mobile browser and install AdNauseam or other adblocking browser plugin, but AdAway covers more ads and is better, though it requires root.
For writing articles, papers, presentations/slides, books, even letters, I recommend Pandoc. It lets you write in Markdown, which is a very nice way to represent text content, but at the same time leverage the powers of Latex for typesetting as well as academic/science stuff like Greek letters.