1) visit this website http://www.hexcolor.in/tools/multipost/index.php
2) login with your facebook account
3) now follow all the requirement and you will see something like that
4) you will see all your fb group and a box fill your message and tick all group click on post
5) you have done it :)> !!! NOTE: DONT TRY MORE THAN 2 TIMES IN A WEEK BECAUSE REGULAR USAGE MAY BLOCK YOUR FACEBOOK ACCOUNT....!!!!