Sometimes I want to use my SSH keys from remote server. But for security reasons copying SSH keys is a bad idea. Fortunately there's a better way to do this - ssh-agent daemon. ssh-agent holds privates keys in memory and allows to authenticate over network. When I ssh to remote server, I can forward ssh-agent connection. Thus remote server will be using my local ssh-agent to authenticate connections.
However, every time I want to forward ssh agent, I can't remember how.
Actually it's as simple as:
eval `ssh-agent -s` ssh-add ssh -A email@example.com