You can specify options (such as enabling X11 forwarding) for specific hosts by adding entries to your ~/.ssh/config file. A typical entry would look like this ( things you should change in italics):

Host nickname

ForwardX11 yes

User username

Hostname remote_host

Where the following substitutions should be made:

Host nickname

This is an identifier for this ruleset. It can be the remote hostname, but it doesn't have to be.

ForwardX11 yes

This turns on X11 forwarding without having to specify -X on the command line. Override this with -x (lowercase) on the command line.

User username

This is your (Unix) user name on the remote machine. If your user name is the same on both machines, you don't need this entry.

Hostname remote_host

This is the real host name or IP Address of the remote machine. You do not need this if you used the real name in the Host entry.

This should be enough information to get you going with X11 forwarding over SSH. For a complete list of entry options see the missing ssh_config man page.