Let's say, for example, you're researching the keyword "how to start a blog" for an article you want to create. "Blog" can mean a blog post or the blog website itself, and what a searcher's intent is behind that keyword will influence the direction of your article. Does the searcher want to learn how to start an individual blog post? Or do they want to know how to actually launch a website domain for the purposes of blogging? If your content strategy is only targeting people interested in the latter, you'll need to make sure of the keyword's intent before committing to it.
Companies that employ overly aggressive techniques can get their client websites banned from the search results. In 2005, the Wall Street Journal reported on a company, Traffic Power, which allegedly used high-risk techniques and failed to disclose those risks to its clients. Wired magazine reported that the same company sued blogger and SEO Aaron Wall for writing about the ban. Google's Matt Cutts later confirmed that Google did in fact ban Traffic Power and some of its clients.
The higher the search volume for a given keyword or keyword phrase, the more work is typically required to achieve higher rankings. This is often referred to as keyword difficulty and occasionally incorporates SERP features; for example, if many SERP features (like featured snippets, knowledge graph, carousels, etc) are clogging up a keyword’s result page, difficulty will increase. Big brands often take up the top 10 results for high-volume keywords, so if you’re just starting out on the web and going after the same keywords, the uphill battle for ranking can take years of effort.
A website or URL’s ranking for keywords or keyword combinations varies from search engine to search engine. A domain may rank for a certain keyword in the top 3 on Bing, but not even be on the first page of the Google search results for the same keyword. Of course, the same is true of all search engines – Bing, Google, Yahoo and every other search engine uses its own method for calculating rankings and therefore ranks websites differently.
One concern we hear frequently is whether it is beneficial or harmful to repeat keywords. In other words, should we vary keywords (dog food, puppy food, and Purina) or repeat keywords (dog food reviews, dog food comparison, and dog food rankings.) The short answer is that the repetition is just fine, as long as the meaning of the phrase as a whole is sufficiently varied. In other words, dog food and dog food online are basically synonymous, and the content that one might expect to find associated with both keywords is the same. However, dog food reviews and dog food comparison indicate somewhat different content and therefore are appropriate to be used in tandem as keywords.
So: how to proceed? On the one hand, SEO best practices recommend that you include relevant keywords in a number of high-attention areas on your site, everywhere from the titles and body text of your pages to your URLs to your meta tags to your image file names. On the other hand, successfully optimized websites tend to have thousands or even millions of keywords. You can't very well craft a single, unique page for every one of your keywords; at the same time, you can't try to cram everything onto a handful of pages with keyword stuffing and expect to rank for every individual keyword. It just doesn't work that way.