How to edit .xsession?

[shiyao ma <i@introo.me>]

I touched a file .xsession in ~ however, it seems lightdm won't let me login if the .xession exists.
Once I delete .xession, everything becomes normal.
Then, how to add .xsession properly?

Thanks.

-- 
My gpg pubring is available via: gpg --keyserver subkeys.pgp.net --recv-keys 307CF736

More on: http://about.me/introom