While it’s important to refrain from “stuffing” keywords, using your primary keyword(s) in the first 100 words proves to be an effective SEO strategy.
Google’s algorithm is something none of us will likely ever fully understand, but there is evidence that the copy / words towards the beginning of your post have some additional weight.
Besides making sure that your primary keyword(s) (or keyword phrase) is in the title, a good rule of thumb is to repeat it again within the first 100 words of the body copy (with the ‘<p>’ tag).
This is easy to do in a natural way, as the first 100 words is usually your introduction to the post topic, and working in the keyword or phrase can be done in a natural voice (eg. ‘I’m going to explain why I think you should buy used fishing gear online, instead of new from the store’ if your target keyphrase is ‘used fishing gear’).
To be sure and practice what I preach, you can see that this article (even though I don’t expect it to rank in search engines) uses the keyword phrase (the title of this post) in the first 100 words.