When the site is new and it has just been created, the owners will invest in doing some SEO, and then think that everything is done. But just like marketing in the real world, SEO is not something you can do once and then forget. Instead, it is a continual process which has to be done over a long period of time, often the entire life of the site. This is because the web is not a written encyclopedia, it is a medium that changes constantly. New competitors appear, search engines change their algorithms, new opportunity for marketing appear, and links that used to be good can become stale and not that important anymore. By constantly keeping an eye on your SEO efforts you ensure that your ranking does not drop, and you can keep focusing on new techniques that may prove to work better.
SEO usually costs time and money, and as such it is unrealistic to think you can do everything possible in every facet of online marketing. So often you have to make choices, and some may be tempted to focus on link building instead of content. However, the goal of SEO is to bring good traffic to your site. Quality is very important, not only quantity. Not having good content means your site has no value to anyone, and as such it will quickly lose any benefit that the extra links gave you. In fact, the most useful backlinks are usually not those you have direct access to. They are reviews from celebrities in your niche, news sites, and anyone who already is an authority talking about your product. By having good content, those links can actually come by themselves, simply through PR or word of mouth. But a bunch of backlinks on low authority blogs will not help you much at all, and the ranking you may get from them will not last long as those sites clean up those links. Instead, focus on your audience and try to know who you are writing for. By producing good content you are helping your site more over the long run.
This is very important for SEO. Keep in mind that the search engines are just large computer programs digesting your site and trying to figure out what it is about. One of the simplest things they do is to count up all the words and look for repeats. They then calculate percentages, or densities, of specific 1-word, 2-word and 3-word phrases that are found in your text. By looking at the most popular keyword phrases, their programs understand the important themes of your page. If you observe your own writing on a specific subject, you will see the patterns as well.
I don’t recommend that you write solely with keyword density in mind as it will result in lower quality content. However, I also don’t recommend that you completely ignore keyword density in your content creation. My preferred approach is to write content straight-up for the first draft. Then, as you edit for grammar, consistency, and clarity, also edit for density. Run your content through a density checker and see what phrases are used the most. Make adjustments accordingly so that your top themes / keyword phrases are showing up between 2-4% of the time. But don’t do this to the extent that anything reads as unnatural. You need to always keep your audience in mind.
This tag used to get a ton of play for SEO, but is now largely ignored by the search engines. I believe it fell out of favour due to manipulation and misuse. It is a tag that is not seen by the end-user, so unscrupulous web masters abused it and it became less-and-less important for SEO. Real SEO tactics don’t abuse or deceive. I still populate my keyword tags because I believe they are still looked at, but I don’t believe they are very critical. If nothing else, it’s another instance of your keywords. They all help SEO.