Suggestion for web contents

Can anyone tell me what are the most important factors to be considered when writing contents for a web page to make it unique with proper SEO?
And also how to write articles for article directories that accept in most cases?
Please help me with your better suggestions.

Four words for you. Content that benefits readers.

Of course a keyword density of 2%-3% is recommended. I also suggest that you do some light keyword research to see other ways that you can improve the SEO within the content. However, the best thing is to write content that will benefit your readers. This can include providing accurate info, using heading, and many other techniques that you can find out about online. Probably even here if you look even deeper.

should be 100% unique,
key word density should not be lower than 4%.
informative and useful to the readers..
perfect grammar and coherence,

goodluck mate!