You need to have your keyword at least once in your content. Don't worry about squeezing it in as much as you can. Keyword density has minimal impact in Google's algorithms today. As long as you use the keyword once in the content you are good.

I try and do this in the first paragraph. I do this for a couple reasons. First, you are talking about your keyword in the article and in the introduction you are supposed to talk about what you are going to talk about. See how that comes full circle? The other reason is so I can write naturally after the first paragraph.

Just make sure to work the keyword into the content at least once and then for the rest of the article you can write completely naturally without worrying about keyword SEO.

Here is my example for the keyword "How to lose weight fast":

Trying to lose weight can be very frustrating. There are so many methods out there that claim to work, but many of these "methods" are actually just scams trying to take your hard earned money from you. If, like many other people, you are trying to figure out how to lose weight fast, I have a great trick for you.