Handy shortcut when you mistype a command name, in the example below I mistype "rm" as "em"

em /var/log/path/really-long-file-name.log 
em: command not found

$ rm !:1
rm /var/log/path/really-long-file-name.log

Repeating the last command, most of the time you would just use the arrow up key however not all keyboards have arrow keys

$ echo "Hello World!"
Hello World!

$ !!
echo "Hello World!"
Hello World!

Handy shortcut for when you forget to prepend a command with sudo

$ apt-get install sshd
E: Could not open lock file /var/lib/dpkg/lock - open (13: Permission denied) 
E: Unable to lock the administration directory (/var/lib/dpkg/), are you root?

$ sudo !!
sudo apt-get install sshd
[sudo] password for user:
Reading package lists... Done
Building dependency tree
Reading state information... Done

If you want to reuse the last argument from the previous command

$ cat /etc/hosts
127.0.0.1   localhost
127.0.1.1   desktop

$ vi !$
vi /etc/hosts

Cleaning up the terminal

Clear the screen

$clear

Ctrl + l

Stop the standard out of a program from displaying in your terminal but keep the program executing.

Ctrl + s

Ctrl + q

Bash tab completion works with wild cards

$ rm *.txt  <TAB>