how to become a good web content writer

The content writer here. Well, these days I'm more of a copywriter, though I still get assigned blog posts from time to time. My work these days isn't particularly SEO-centric, though we do occasionally have clients request that we incorporate keywords -- usually localised businesses, e.g. contractors, professional painters, roofers, etc.

Anyway, I've been doing this since the beginning of 2014. Here's my general advice:

• Practice will improve your skills. I've always been a pretty decent writer, but when I began writing professionally, my skills definitely improved. Now, there's a limit to this effect, in my opinion. High-volume SEO content writing will improve your skills to a point, but over time, you'll start seeing diminishing returns in that regard. At least, that was my experience.
• Don't write in a way that's too academic, stilted, or formalised. I was fresh out of being a college student, and I've noticed that my very early work comes across as a bit cold and stilted. Over time, I learned to write conversationally. Obviously, your tone and style will depend on the industry, niche, or brand you're writing for. A B2B SaaS company has a different brand identity and personality than a T-shirt company aimed at 18-22-year-olds.
• Don't keyword stuff. This probably goes without saying, but I've noticed that even over the last 2-3 years, there's been a shift away from shoehorning keywords into the text. Some long tail keywords can be quite challenging to work with, but I don't advise incorporating a keyword in a way that sounds unnatural. You want the prose to flow naturally and sound genuine.
• Know your audience. This is a bit of a "general marketing" thing, but when you write, you should write as if you're addressing people. Who are they? Are they high-level C-suite execs that appreciate formality, don't mind complexity, and respond well to relevant jargon? Or are they middle-aged housewives looking for a miracle diet pill?
• Target the right people with the right solutions. Let's say you're a professional cleaning company, and you want to create a nice, engaging, well-written blog post about "toilet cleaning." You could write about DIY tips, sure, but that counteracts your brand's goal -- to encourage people to use your service. I've done quite a bit of content for those kinds of companies. You don't want to attract DIY-ers who want to save money by doing it themselves. You want to attract people who are looking for a pro cleaning service.
• Talk about them, not about you. This applies to blog posts, but it's even more relevant for website copy, e.g. service pages or your homepage. Frame it in a way that highlights their problem, one they can relate to. Then, talk about the solution you offer. Make it about your customers and what they need, not an excuse to brag about how great you are.

Additional tips

1. Learn proper English.
2. Research.
3. Read your stuff out loud.
4. Have other people read and critique your stuff.
5. Write about a lot of different topics.
6. Use an Oxford comma.