How to write a autostart script for gnome

I want to automatically run a program when I log in gnome. How to write a autorun script for it?

Here is one example:

$ cat ~/.config/autostart/dropbox.py.desktop 
[Desktop Entry]
Comment[en_US]=
Comment=
Exec=/home/zma/bin/dropbox.py start
GenericName[en_US]=
GenericName=
Icon=system-run
MimeType=
Name[en_US]=
Name=
Path=
StartupNotify=true
Terminal=false
TerminalOptions=
Type=Application
X-DBUS-ServiceName=
X-DBUS-StartupType=
X-KDE-SubstituteUID=false
X-KDE-Username=

To set up a new one, you can just copy this file and change the “Exec” field.