Keyword usage or keyword density has always been a talking point that doesn't a very clear answer. If you have experience writing content on Wordpress for example, then you may have used the plugins along the likes of 'Yoast SEO'. This plugin uses a traffic light system that tries to steer you in the right direction when writing an article. While this is a useful feature and it does give you some good actionable tips it also gives a lot of false positives. This then creates a problem for you and you may sit stressing over the finest details when in fact they won't make the slightest difference.
There's no right or wrong answer hear in my opinion, you may hear some people say a fixed number or a certain ratio but you really just need to use some common sense here. If you have written a 500-word article don't go including your keyword 50+ times. This will be very quickly picked up by Google as keyword stuffing and on top of that, the article most likely won't read well at all. Likewise, don't only include it once throughout the entire article, Google again will find it hard to determine what the piece is actually about.
When writing content you want to make sure it reads well first and foremost, get into the mindset of writing for the user and not the search engine. Just make sure you mention your keyword regularly throughout the article where it feels natural for it to go. There's also a debate as to whether mentioning your keyword early in the article makes a difference. Whenever writing content for a website I tend to include the keyword early anyway as it more often than not tends to make sense.
When writing the content for your site or clients try to think about things such as:
- Does the content read well?
- Is my content long enough?
- Is there a mix of content and images, videos etc?
- Is the content Unique?
- Have I included my keyword regularly enough in my content?
Having a good piece of content that ticks all of these boxes can take you a long way and will outrank a bad piece of content that happens to have the perfect keyword density ratio.