Brian, I have a burning question regarding keyword placement and frequency. You wrote: “Use the key in the first 100 words … “. What else? I use Yoast and a WDF*IDF semantic analysis tool to check the content of the top10 rankings. Pretty often I have the feeling I overdo it, although Yoast and WDF/IDF told me I use the focus keyword not often enough.
Another excellent guide is Google’s “Search Engine Optimization Starter Guide.” This is a free PDF download that covers basic tips that Google provides to its own employees on how to get listed. You’ll find it here. Also well worth checking out is Moz’s “Beginner’s Guide To SEO,” which you’ll find here, and the SEO Success Pyramid from Small Business Search Marketing.
When would this be useful? If your site has a blog with public commenting turned on, links within those comments could pass your reputation to pages that you may not be comfortable vouching for. Blog comment areas on pages are highly susceptible to comment spam. Nofollowing these user-added links ensures that you're not giving your page's hard-earned reputation to a spammy site.
Analysis is the key to SEO – Monitoring your ranking on search engines is key to getting better results. Start by tracking the most important website metrics to set a baseline for your performance. Make small content changes and see if you notice a boost in your site traffic or rankings. Avoid making several unrelated changes simultaneously so you can always keep track of what was responsible for improved performance.
Simple navigation reigns and quality content is king – A user-friendly website, with interesting and easy-to-find information is what will boost your traffic. Each page needs to be built around keyword themes, with unique content, so search engines can easily index yours and rank you higher. Positive behaviors from site visitors is your best bet for a better ranking, so keep the content natural and focused; avoid jargon and keyword stuffing to keep users from leaving the site unhappy and hurting its ranking.
So if you think about it, SEO is really just a process of proving to search engines that you are the best site, the most authoritative, the most trusted, the most unique and interesting site that they can offer to their customer - the searcher. Get people to talk about you, produce good quality content, get people to link to you, and Google will be more confident that you are the best result that they can offer to their searchers, and that’s when you will start ranking on the first page of Google.
Another example when the “nofollow" attribute can come handy are widget links. If you are using a third party's widget to enrich the experience of your site and engage users, check if it contains any links that you did not intend to place on your site along with the widget. Some widgets may add links to your site which are not your editorial choice and contain anchor text that you as a webmaster may not control. If removing such unwanted links from the widget is not possible, you can always disable them with “nofollow" attribute. If you create a widget for functionality or content that you provide, make sure to include the nofollow on links in the default code snippet.

Optimizing a website may involve editing its content, adding content, and modifying HTML and associated coding to both increase its relevance to specific keywords and remove barriers to the indexing activities of search engines like Google ,Yahoo etc.[citation needed] Promoting a site to increase the number of backlinks, or inbound links, is another SEO tactic. By May 2015, mobile search had surpassed desktop search.[3]