Please review my following site Free Seo Tools what kind of on-page SEO I can do to increase my Serps?
Internal pages should allow links to be dofollow. It is the only way for you to distribute page rank and value to your internal pages. So, categories are nofollow now, and this is not so helpful. If you are worried of duplicate contents because using similar keyword and tags, try to use canonical tag. You can implement canonical by default using All In One SEO pack if you use wordpress (I assume you are using). Most of you posts are not utilized to point internal pages. I'm looking at your keyword where you have great potential in "free seo tools" But, none of your recent articles pointing to your site using this keyword in contents. Point your targeted keywords with its appropriate URL in all your articles to increase the value of interlinking and increase current ranking.
It's all about search engines basic criteria so you have to do that some like : Title, meta keyword, description, site map, roboot, h1,h2 many more...for increase SERP before doing off page.