There are a few key things that are critical to
SEO on your website.
Do you have blog? Write fresh content on a consistent basis. Once a week or so - but be consistent. Don't write 20 blogs one week and then wait two weeks and write only a couple. Better to do a blog only a couple of times a month, consistently, than to slam and then drop.
Be careful not to "keyword stuff." I mention this because you said you think you might need more keywords. Having the right keywords and use thereof is, overall and while important, is a pretty small piece of the pie. Using your keywords too much will have the opposite effect and in some cases get people unindexed altogether.
One of the biggest parts of the pie, and one of the biggest ways to improve
SEO is through creating backlinks. Google wants to see a popularity factor. It wants to see that people are interested in what is happening at your site - and backlinks and blog comments lets them know that. You will want to do this through a variety of ways - and it will seem overwhelming at first - but set up a system and have your checklists and procedures in place and it will become a cinch very soon. Be sure to always be analyzing results.
The other big piece of the pie with regard to what makes up
SEO is longevity. The longer you have your domain registered, the more reputable you appear, and so better results. When you register your domain they recommend registering it for at least 2 years. 3+ is better because it shows Google you are not fly-by-night.
Look at websites like SEOMoz for more details. Google - as facebook and others - change their criteria and rules alot and SEOMoz is great at keeping up with it - and they seem to be the premier resource and authority that everyone should have in their arsenal.
@ April - I don't know if you noticed or not that the information in the link you provided is quite old and so while some of it is probably good information, it may not apply. What it was like 4 - 8 years ago has likely changed a lot. I don't mean to call you out - and I do that often where I find something and then after spending a lot of time reading and researching I then notice that the information may be outdated, simply because of the copyright, so I hope you don't feel I'm picking on you at all.
Hope this helps.