If you use .rhosts files, ensure that they have the strictest possible permissions.
Create the empty file /etc/notrouter if you don't want your server to act as a gateway.
Disable all the network services you don't actually need by editing /etc/inetd.conf to decrease the risk of unauthorized access.
Tighten network security by enabling secure RPC within products such as NIS.
Avoid the use of NFS to prevent remote machines from having access to your filesystems, unless necessary.
Make use of firewalls to control remote access to your servers.