(Following are some ways I know to ensure privacy and avoid someone spoofing your identity.)
First, I'll recommend registering yourself with a nickname so that no one can steal your identity.
Use this nice tutorial to register your nick on freenode. Other services will have their how-tos.
Second you might want to disable FINGER, TIME and VERSION requests.
FINGER enables getting personal information like Email. TIME gives out your location information and VERSION gives out the OS and client names and versions you are using. Knowing the versions, an attacker might try a specific exploit.
Here is a nice tutorial to do it in xchat. Look at the client specific documentation if you use a different client.
Also, you might want to hide yourself from the global who/whois list (The way to do it on freenode is:)
(+i = invisible mode)
Leave a comment if you know a good addition to this list.