In your WordPress admin area, click “Options” and then click “Permalinks”.
Select “custom” in the Customize Permalink Structure area and in the box next to “custom” enter this:
/%category%/%postname%
This will create URLs for your permalinks and archives that would look like this:
http://yoursite.com/yourcategory/title-of-your-post
Click “Update Permalink Structure” to save above setting.
Now you are done.