Found this detailed and straight sell answer by Suvashree Bhattacharya, Digital Marketer at REVE Chat, to the question, What are some good tips on copywriting? on Quora.

Understand your product first and define your positioning
Before writing a website copy, understand the product first and decide how you want to position it. You should have a clear vision of what exactly you are offering to your customers. In your copy, both should be reflected.

Know your target audience and their pain points
The 2nd step in copywriting for websites would be identifying your target audience and their specific pain points. So, firstly target the segment of the people you want to reach and understand their issues.

Suggested Read: Why UX Writing is Crucial to Your Design Process

Convey your key selling points first
Through your copy, basically, you need to build up a situation. First, mention what problems your customers are having and let them know that you have the solution. Through the copy, describe the key selling points in such a way that they actually are convinced with the idea that you have a complete understanding of what they are going through.

Develop an emotional connect
Next, develop an emotion which will work as a powerful motivator. Through the storytelling, make them imagine a life without that problem. Positive emotions are usually preferable, but the negative ones like the fear of experiencing something bad many times work.

Read the rest of the answer on Quora.