Is there anything legal you should think about? Is there any special urls you need to have? Can you and or should you protect your wordpress plugin? with code? I see many people copy other people plug in and use this kind of license? This program is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License, version 2, as published by the Free Software Foundation. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program; if not, write to the Free Software Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA */
You need to have knowledge of PHP, if you know PHP well, go to Wordpress codex and read the tutorials.
These are the best i have seen. go through the links below and writing a plugin isnt that hard. http://corpocrat.com/2009/12/27/tutorial-how-to-write-a-wordpress-plugin/ http://corpocrat.com/2010/12/05/10-best-tutorials-for-wordpress-plugin-writing-development/