Lets see some of the shortcuts that will be useful if you are using Ubuntu 18 and want to save a lot of time.
Ctrl + Alt + T => Opens terminal
Ctrl + Alt + L => Lock the screen
Ctrl + Alt + D => Switch to Desktop
Alt + TAB => Switch between applications
Alt + F2 => Open console(type something like gedit there)
Ctrl + Q => Exit the active application
Ctrl + Alt + Del => Logout of the current user
I am hoping these shortcuts would help us a lot. If you have any to add comment out in the comment section that I will add for sure.