Your content on your website is your sole communication channel that helps you reach out to your customers and clients and engage them meaningfully. For this you need to create effective content, but what is effective content?
The small answer would be content that gets you results, whatever the desired results are. The complex answer involves strategy, execution and persistence.
Strategy means knowing exactly what you should be publishing in order to increase your business or effectiveness. For this you have to understand your audience: what it wants and what are its aspirations? After figuring out what they are looking for, provide them.
But sometimes it is not possible, even not feasible, to provide content that they are looking for. Sometimes you have to provide something totally new, something totally alien to them, but still it is highly useful once they begin to use it. This comes under long-term content strategy where you build up a long lasting relationship with your readers or viewers so that they pay attention to even your blurry and oblique messages.
Read this interesting checklist on how to create effective content for your website (it is a book review, actually).