first thing you should be keep in my mind that what the latest trends is going on. After that make research about what actually you want to write for the seo that never published and write by someone else. After that make a raw content about it & get refereced from top sites.
When you are going to write an article for seo purpose then always keep one think in mind ""Keyword density"" which is most important part to notice in article and along with that which article you are writting it should be unique and organinc.
Well, writing articles needs some basic content quality skills. The content you are going to writer should be relevant to the website you are linking with and content should not have any grammatical mistakes.