Then we have to wait till the links get disavowed. After that we need to create several web 2.0 pages that will contain a link of the penalized site. Then we need to start optimizing those web 2.0 pages. Optimizing web 2.0 pages will increase the ranking for both the page & the penalized site. Thus traffic will increase for the penalized site.
What we should do so that a site doesn't get penalized?
1. We need to create Quality Back links.
2. Creating Bookmarks from PR 2 or higher sites.
3. Directory Submission from PR 2 or higher sites.
4. Need to Publish Press Release At least once a Month
5. Need to Publish At least two Articles in a month
6. Need to publish at least two Web 2.0/ Blog post in a month.
7. If you are targeting to getting links from Forum, then you need to invest some time regularly on that forum. So that it seems you are really giving a value to the forum. (Otherwise don't post links to forum).
8. Never comment on any relevant blog that has already published 50 comments on its page.
9. Try to focus on developing Good Content so that both Reader & Search Engine Likes the content.
Note: PR 2 is for domain, not for the pages you are linking to.