When you have access to a user account on a server, it will often display a banner upon login indicating the IP of the last user.
To mitigate such a giveaway, it is often prudent to hide your IP from this message.
Please note that this technique will not erase the bash history, nor will it remove your IP from logs, it will just look less suspicious to the account owner.
Firstly, ssh to the box in question.
$ ssh [host] -u [user]
Now, on the target box, execute the same command to SSH to localhost or the external host.
$ ssh localhost
Re-enter your login details and you are done; the last login will appear to have come from localhost