Everytime I have to setup a new gnome shell I forget these two important settings:

gsettings set org.gnome.shell.app-switcher current-workspace-only true

gsettings set org.gnome.shell.overrides workspaces-only-on-primary false

The first one is to have alt+tab listing only the windows in the current workspaces, while the second one is to enable workspaces on the secondary monitor.

The first one is essential for me to work with Gnome workspaces, while the second one is a nice to have and it would be great to be able to switch it on/off without logging out..