Internal linking can greatly improve your rankings. Every time you add content to your website, you need to link this content to pages that has content relating to the specific products/service that you mention within your post.
Using the sidebar to link other pages is also a great option. By passing a lot of internal links to other pages, it tells Google that you value a particular page and feel it’s important. Google will see that you are putting a lot of emphasis on that page, and rank that page higher than other pages.
It is important to keep these links visible, and not hidden. Make sure the link is visible and on every page of your website.
Essentially all you have to do is follow 2 steps,
1) Link within your content – Don’t always use the same keyword in the anchor text, make it natural, and not the keyword you want to rank for. By making it more natural Google will notice this and rankings will not drop.
2) Make sure you re linking to your most important pages within your side bar on every page of your website.
If you follow these steps you should see a positive difference in your rankings through internal linking.