Follow this procedure from the beginning, without skipping any steps. Make certain that each step is completed correctly or find out why, since the following steps depend upon the earlier ones being right. If you cannot get a step right, stop and ask here and we will try to help. http://www.parktool.com/blog/repair-...ur-adjustments

There is a link to rear derailleur adjustments there as well, in case you are feeling ambitious.