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Run your site through SEM Rush. It's generally pretty accurate if you need a better understanding of what pages draw traffic and for which queries. After that, it's a good idea to use your analytics tools to identify pages that draw traffic. One really good link may be driving a ton of traffic to a specific page, but it may not necessarily rank very well. The site might lose a significant amount of referrals due to that link. So make sure to check where your referral sources go as well. When all of that is said and done, it's time to look at links. Use a few different sources such as Webmaster Tools (Google and Bing), Majestic SEO, Ahrefs and OSE. Majestic and Ahrefs are the favorites, as far as percentage of links and freshness. When you have the Keep and Cull list, make sure to redirect the keepers to relevant pages. If the page was about donuts, send it to the new donuts page. Don't send it to the bagels page. Google dislikes that. Blanket redirects are generally sub-optimal. As for the culled pages, you might try to offer a useful 404 page. Something that helps them find something similar to the topic of the page that went away. When all of the dust clears, 410 the culled pages. Alternately, you can skip straight to a 410 if you're only worried about bots wasting crawl budget on a bunch of 404 results.