Usally, uBlock Origin's default configuration is all you need. If you stumble on bad stuff still, this is for you.
Before we begin, i recommend to read the official wiki first.
Find out what any of the popup UI means
How to open the dashboard and what the settings do
What this guide is all about: Filter lists
Click uBO's red shield icon on your toolbar, then the 3 gears icon to open the dashboard. On the "Filter lists" tab you will see a assortment of lists for you to enable as you see fit. Here are some recommendations:

If you visit websites that don't speak English: Enable the lists under "Regions, languages" that fits your needs.
Still getting badware? You might want to give custom block lists a shot. Click uBO's red shield icon on your toolbar, then the 3 gears icon to open the dashboard. On the very bottom of "Filter lists" tab you will see "Import..." that let's you paste URLs containing such lists.
This is a collection of reputable and up to date filter lists that blocks virtually everything.
Is virtually not enough for you? Me neither. On this filter list of mine i add bad stuff as i come across them.
Beware: Since i'm new to this, there is NO guarantee that i won't break stuff on your end. Please let me know if i messed up.
If you have trouble sanitizing embedded devices like FireTV that doesn't let you install uBlock Origin, and you happen to have access to your routers control panel, try DNS blocking.
Read the official reply to Manifest V3 for uBlock Origin here
If you use a Chromium based browser such as Chrome, you will find that they disable V2 extensions like uBlock Origin without your consent to allegedly protect your security. So, what are the options?
Also: Thorium - MV2 will remain - Thorium is another excellent Chromium based browser that comes with uBlock Origin.
What is the best option here? This is hard to say. As for Brave and Thorium, it depends on how difficult restoring MV2 support is on a technical level and how much effort would be required to maintain it and keep it fully functional. The creator of uBO will continue to maintain the extension itself.
If you want my opinion: Any Chromium browser with uBO Lite for stuff that needs Chromium to work, Firefox for anything else. These are the 2 things I'm positive will work for the foreseeable future. If you're comfortable with trying a different ad blocker, Brave's Shields is pretty reliable for me on mobile.
https://github.com/yokoffing/filterlists - a great uBlock guide - you should check it out!
https://firebog.net/ - they list interesting filter lists
https://dnsforge.de/ - should watch out for the filter lists they use, thats how i came across StevenBlack
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