Here I'll describe how to be able to ssh to an AWS instance, as well as any other server, just by typing:

$ ssh your-server

First, make sure your private key is in ~/.ssh/ with proper rights set. Then create ~/.ssh/config file with the following content replacing host names and key location with your own, appropriately:

Host your-server
  HostName your-server-hostname-or-ip
  User ec2-user
  IdentityFile ~/.ssh/private-key.pem

That's all.