Your copy isn't for everyone, but it's for someone. There is someone out there who is endlessly surfing the internet, wishing and hoping that a product like yours exists. If you can only connect with this person, you have a guaranteed sale. There is no hard-selling or strong-arming; just a little well-written copy.
Before you can write for that audience, you need to know who they are. Copywriters spend a great deal of time researching their audience. You need to do this too.
One way to think about this person is that they're your "best customer." They're not your only customer. But if you aim at the best customer, or the one who most needs what you're offering, you'll get others as well.
It's estimated that for most businesses, 20% of their customers generate 80% of their sales. It's your job at the research stage to discover who those 20% are.
You need to create a demographic profile of your customers. The demographic profile includes quantifiable data about your best customer, like their age, gender, ethnicity, location, income level, and so on.
You also need to take into account psychological data that's not quantifiable. This includes things like attitudes, fears, likes/dislikes, interests, motivations, and so on. This data should include how the person feels about the purchases they make, the companies they buy from, your industry, etc.
From all of this data, you should create a persona of your best customer. You're going to actually create a human being. It will be an imaginary human being, but an important person nonetheless because this is the person you're going to write copy to.
For example: "Will Clark, a guy in the American Midwest in his 30s who works for a mid-sized company. He carries around a little extra weight and he worries it might be having a negative effect on his marriage, but he can't get up the motivation to start going to the gym."
The information that goes into creating Will should come from actual customer data and not just what you think he's like.
This research is quite a bit of work, but it's essential for your copywriting to work. Once you've created a persona, all you have to do is tell that person how your product can help them. This is what makes copywriting work like magic.