There is an old saying in web "Content is the king". Finally what makes or breaks the thing in long run in web is the quality of content. In fact, it's not just the web but any industry which depends on content. Take it to a more abstract level, the make or break in the long run is the content of your actions that will be a huge determinant on the quality of success. There are other aspects like marketing and positioning, which are important but we will not get into here. But the core of everything is the quality of content, if you are looking for a long run. If you are looking for a flash in the pan than other aspects become more important than the content and those are personal choices in terms of handlingsituations.
What are the qualities of a good content
New Insight or new way of presenting
Content written by you with a focus on bringing new insight or new way of presenting the ideas. Don't think that you have to invent on everyday basis and aim of Nobel prize. At times putting things in a simple way, so that it brings the various aspects on the topic that your are writing on comes out more clearly.
There are many people who have written History books. But should it stop new authors to write on History. No because people do keep getting new insight on the way History has happened. Present context also leads to new way of interpreting old happenings. It's like a layered thing. When one peels a layer, the world get exposed to the underlying layer. New set of people come and interpret the new layers and that keeps on happening.
The other thing is to present the idea in a simple way. For example in Hindu Mythology original Ramayan was written in Sanskrit. Not many people could understand it. In 16th Century, Tulsidas wrote the same content in Awadhi, language spoken by masses. And the religious piece of work got accessible to everyone.
Write for Human and not for Search Bots
Content written for a human user and not search bots. Write for yourself so that you learn more about topic. I find writing about things a great way of self learning, as the process of writing helps in building a structural framework to think about the topic.
This does not means that you should not understand how search engine works. If you are driving on a road you want to know all the rules and regulating of driving. But that should not mean that you stop enjoying driving. Enjoy the process of writing and things will fall in place.
There is a whole lot of theory around how search algorithm works. From the keyword placement to keyword density and what not. Have awareness about them but don't get driven by them. It also means that you might want to choose words which make your writing simple and easy to understand as these are the words humans will use to search. If you are writing, then definitely you want to be read. Have the right balance on that front. You don't want to create a masterpiece which no one is going to look. There is a fine line between right dose of marketing and positioning compared to blatant shouting about your content.
Content as Notes to self
For me this is the most relevant thing. In olden days, we used to take notes in our notebooks so that we can refer to them back again. I consider my blog as a way of keeping notes for myself in the future. Many times we had to research a topic to solve a problem and in olden days we used to scribble those in our yellow parched notebooks for reference in future. Blogs make it much easier. Only thing I have to write and put things in such a way that it is comprehensible in future. And search engines are there to quickly search the stuff.
Write content that you yourself feel like going back to refer in future, when you want to recollect your thoughts.
Content written by you and not Computer Generated
Content which is not computer generated or scraped arbitrarily from different web pages. What is the probability that among a million monkeys with a computer, one of them will turn out "Romeo and Juliet". If you are really want to copy everything from another web page as a reference better bookmark that site. There are on-line bookmarking services which can help to access those bookmarks from anywhere in the future.
For me a good benchmark of a content is that after writing a post, I get a feeling that I know more about the topic and understand finer points on the subject. Feeling of an Einstein on that particular area. This means quality research time spent on understanding and learning more about that. You may be a guru already on the topic but putting the thoughts in a format so that it can be used by others itself requires good amount of work. You yourself will realize that many finer points which you have taken for granted till now, actually deserved more attention. If nothing else, you will hone the art of communicating your thoughts to others in a better way.