How do you develop rich web content writing and other material for your demographic? Research! In depth research about your client or customer should always form a part of your marketing or content writing plan. Otherwise you may be anticipating needs and wants that may not even fit your demographic. Ask them: through surveys, focus groups, feedback, industry research etc what they really want to know, what they are feeling as part of the customer journey and what they need and meet those needs for them.
Engaging readers and customers is a life long journey
Although this depends on the industry, a good marketing campaign should be ongoing and nurture the customer/client every step of the journey, from before the decision making process has even begun, to post-purchase and beyond. The term "life long" refers to the life of the customer journey, rather than the life of the customer, although in some cases this can be one and the same. For example, if you had a product or service that your customer requires from infancy to old age, then you would adapt to suit their changing needs throughout their lifetime. An example of this might be a medical/doctor service.
...life long" refers to the life of the customer journey, rather than the life of the customer...
Content writing needs to be fresh but reusable
Again, this is industry and topic dependent but well written content is usually evergreen or at least, able to be repurposed. If it’s news content that is being uploaded straight to a website, for most clients the content can stay on the website perpetually— unless it harms the company (perhaps there has been a change in research or they no longer offer the product or service) there’s no reason why it cannot be archived. In terms of fresh content, it really does depend on the client’s audience. Some may be content hungry and others are “slow burners”. As long as fresh content writing is going out at least weekly (for most industries), then it depends on the audience.
So make sure when you're embarking on content writing that a majority of your content is going to be reusable or can last for a year or longer. It also pays to make sure you know what you are writing and what your audience expectations are.