(this applies to a non-standard xfce setup)
See the xfce web site.
Also visit the zentile web site.
Tile current workspace ~ Ctrl + Shift + t
Untile current workspace ~ Ctrl + Shift + u
Cycle through layouts ~ Ctrl + Shift + s
Go to next window ~ Ctrl + Shift + n
Go to previous window ~ Ctrl + Shift + p
Increase size of master windows ~ Ctrl + ]
Decrease size of master windows ~ Ctrl + [
Increment number of master windows ~ Ctrl + Shift + i
Decrement number of master windows ~ Ctrl + Shift + d
Appfinder ~ Alt + F3
xfce4 display settings --minimal ~ Super + P
Desktop Menu ~ Ctrl + Escape