In all honesty, you want your articles to be 100% unique. Using copied/spammy/cheaply spun content isn't going to help you in the long run.
There are a few ways to use keywords in article. Everyone has their own "ratio" that works best, I've seen some people say 1% density, some say 3%, some say 1.5%, it all depends.
Here are some good ways to use keywords though: Mix up anchor text that you use while still being relevant
If you want to use the keyword "organic bananas" you can try it like this:
1. I like purchasing my organic bananas from blahblah
2. If you are looking for the best quality organic bananas, don't fall for marketing gimmicks
3. Many people believe a healthy lifestyle comes from consuming healthy, organic fruit, such as bananas