What are some good free websites or guides that offer information on SEO?

There are a numbers of site to gather informations on seo and you also can get a numbers of article written on this ground. You should learn on backlinking, web designing, SMM, PPC and also in seo writing. Seo firm has huge writing and rewriting tasks. Yes there are major differences between this two types of writer. A seo writer need to build his content for various websites which must to be seo optimised. Therefore he need to write things with good keyword density. Besides, he need to search good keywords, as it can help his website to get ranked at a higher position at the search engine.