If you've pushed the line with optimization techniques and have been dinged by Google, Matt Cutts offers advice on how to get back into the search engine's good graces. Matt says it boils down to two basic things:
Fundamentally, Google wants to know two things: 1) that any spam on the site is gone or fixed, and 2) that its not going to happen again. Id recommend giving a short explanation of what happened from your perspective: what actions may have led to any penalties and any corrective action that youve taken to prevent any spam in the future.
Follow Matt's guidelines and with luck your site will be reinstated in Google search results in anywhere from 2-8 weeks.