The short answer is YES. Internal links are very important when it comes to SEO, and association of words, get them wrong and it can really start to screw your ranking positions.
What we suggest is to assign a "keyword phrase" to each page of your site. Any time you use that phrase in your site, link back to that particular page. So if you have a bunch of pages, put it into an Excel sheet so you can track what words go where.
You CAN have multiple phrases going to the same page, but we would recommend that they're similar. In the following case, I want to rank "dog bed", specifically for the small dogs;
- small dog bed
- tiny dog bed
- dog bedding
- small dog beds on sale
- extra small dog bed
Each of those can go to your dog page if you're talking about small dogs and bedding.
Notice I used "keyword phrase" rather than "keyword"? This is because the chance that you're going to rank for "dog" is very very small. "dogs" has more than 732 million results in Google. "small dogs" has more than 15 million results, and "small dog bed" has more than 1.2 million results.
But results are one thing, searches are another. "dog beds" gets searched about 46,000 times per month but "small dog bed" gets about 500 searches a month. So choose the longer keyword phrases when they match your intended audience.
As a rule of thumb, the keyword phrase that you want to rank should adhere to each of the following:
- Should be in the Title tag of your page
- Should be in your description meta tag
- Should be in Schema Markup (if you have products on the page)
- Should be in the H1 title of your page
- Should be within the first 100 words of your page
- Should be linked from your home page content EXACTLY (anchor text)
There are more factors such as Alt Tags on images, Keyword Density (how many times the phrase is repeated versus how much text is on the page), and other factors, but in general, the above items will give you a good starting point. Don't worry about bolding or italics, they have very little value.
Any time you talk about "small dog beds", link that anchor text as is to the page you want to rank.
Don't worry so much about your Navigation in the header or footer, Google can ignore those at times. The key area you want is text in the page content itself.
Hopefully, that gives you a starting point.
As always, think of your user and use logic when you're linking things. Do not have a page talking about dog bowls and cat treats and in the middle shove a link to "dog beds" - Google (and your users) will pick up on what you're doing and that's never good.