Most Common Reasons for 404 error page:
- You change your permalink or link structure of your website.
- You removed such a content from your website.
- 301 redirect the link to most relevant post/article.
- If the errors arising due to misspelled link from another domain,you can either ask the webmaster to update the link.or you can use 301 redirection process.
- If there is no relevant articles on your blog related to 404 link,simply leave it.Google will automatically de- index such a pages (or) also you can de-index manually using webmaster removal tool.
- If you have a thousands of 404 error pages in your blog,redirect the pages when ever it possible.Otherwise block bots accessing these pages using robots.txt.And remove them using webmaster tool.