I recently started work for a new client who had been previously in a contract with another SEO company. This has happened many times, sometimes for more advanced SEO but more often than not, because their previous six month of SEO did not yield any results. I have found that two basic parts of SEO are often completely overlooked.
Proper keyword research is one of the most overlooked steps that I have seen. It is also one of the hardest and most time consuming areas if done properly. The mistakes I see when doing keyword research are either the keywords are unreachable because of the competition for them or the keywords are to low yield to be worth doing anything for. I could go on for hours about keyword research but in a nutshell don’t shoot to high, don’t shoot to low and make sure that you have identified if a national, regional, or truly local campaign is what you need. Then start running lists and lists of keywords and checking what the competition is for them and what kind of searches they get. This can take hours. Once this is done trim that group down to a minimal number to start with or a larger group with common parts in them. I usually try to go with five to forty keywords at most with the previous mentioned constraints.
The second major mistake is that the keyword density is not properly met or duplicated on many pages so that it is negated. Keywords can be placed in the copy of the website or in the code of the website in ways such as image alt tags. Getting keywords in your title tag, header one, header two, header three, emphasis, header four, and header five are also good. The trick is to make sure it is very organic if you do things this way. Also make sure that if you use any of these, which you should if you can, make sure that they are not the same on any pages. Duplicate is bad, it negates the effort on both pages.
NOTE: Very often duplicate title tags are done and not noticed. Check EVERY title tag to make sure it is different and keyword rich.
There are many other things involving SEO that could be expounded on but those are the two major mistakes that I have seen very often. If you are an SEO Specialist or just trying to up your ranking on the search engines for the very first time do your best to avoid these two mistakes and study from all the resources that you can find.