'ControlMaster auto' for reusing SSH connections

Just add these two lines to your ~/.ssh/config and you're good to go!

Host ...
    ...
    ControlMaster auto
    ControlPath ~/.ssh/control:%h:%p:%r

Adding those two line at the end of the Host config in ~/.ssh/config will make it so you can make new connections to the same host without needing to type a password. This is very helpful in the instance that you have some kind of dual factor authentication for accessing a system, and it takes too much time to authenticate every time.