Sitelinks are becoming everyday more important in order to maximize the use of your advertising budget. As anticipated in one previous post, site extensions are now available at an adgroup level and can be optimized on a per site link basis other than all together.
A good method to test site links is the following:
This might sound simple and it actually is if you take the time to do it right. You should focus on writing good content that is relevant to your AdGroups and to the landing page you are linking the site links to.