I've been using Debian for probably a decade and set up a couple new installs of bookworm this week. In no particular order, here are a few things you might want to know:

• I find aptitude a lot easier to wrangle than stock apt or the GUI package managers (they're all front-ends to the same thing). It's got interactive queries.
• I never bother with anything other than the netinstall ISO, since nowadays downloading the packages during install is faster (and much more likely to be up-to-date) than reading them from disk. I believe the live CDs have a flashy new guided installer though, which I haven't tried.
• Debian's default graphical environment is GNOME, and if you're coming from Windows there are several options that might be more familiar. I use Cinnamon, lots of people swear by KDE and XFCE, but there are a million Windows-like environments to choose from. That said, if you're sick of Windows, try GNOME :).
• Others have mentioned that the trade-off of stability is that some software can be outdated. My preferred solution (which is not the only possibility) is to keep both stable and testing in /etc/apt/sources.list. Note that by default this will cause you to just pull everything in from testing; this post details how to prevent this if desired.
• Debian 12 has disabled os-prober by default. This means that if you're dual-booting Windows you'll need to edit /etc/default/grub (the comments explain what to do) and run update-grub as root. I also usually end up fiddling with the graphics options to make sure the virtual TTYs (the consoles you access with Ctrl-Alt-F<n>) have the appropriate resolution.
• Debian 12 has moved non-free firmware into its own distribution. This shouldn't be an issue for a clean install, but if you end up with a non-working wifi card or something, check /etc/apt/sources.list for non-free-firmware and make sure you have the appropriate package installed (search ~snon-free-firmware in aptitude).
• Some packages will have interactive setup programs that you can re-run with dpkg-reconfigure $package. I most often use this with console-setup and keyboard-configuration, the former for TTY font size and the latter for swapping Caps Lock with Ctrl/Esc.

Lastly, the Arch wiki is a great resource even though Arch and Debian aren't directly related.