This is often the most time-intensive part of your copywriting.
You need to figure out why people buy the product, how they buy it, what they use it for, and what really matters to them. If you don't have this figured out, you really cannot write a copy that works. When it's your own business that you're writing copy for, things go much faster, of course, as you know the product and the competition.
Gauge the competition
You need to be aware of your direct competition, how they present their product, and what claims they seem to be making. If you are not selling something unique, you are selling as much for your competition as you are selling for yourself. Being "like" others or choosing to be "one of the leading providers of" is a losing strategy.
Neuromarketing research tells us that differentiating our claims is the key to talking to the old brain, the decision making part of our brain. Our whole business identity should be different from the competition, and the claims we're making about our product should stand out.
Get out of the office
The answers are not in your office and you won't have eureka-moments at brainstorming meetings (working solo is far more effective anyway). You have to interview people. Don't waste time interviewing random people, you need to talk to your ideal customers and find out what's on their minds.
Find out what they think about your kind of product, what language they use when they talk about it, what attributes are important to them, and what promises would most likely convince them to buy it. Pick the last 10 to 20 customers (who still remember their purchasing experiences), and ask them these questions (recording the interviews is a good idea, but ask for permission):
Take note of the exact wording they use. Your copy needs to match the conversation in your customer's mind. If you talk about "scribing devices" and he needs a pen, there's a mismatch.
My point is that when customers see the product described in words they have in their mind already, then you've got their attention.