Start by doing some research on your keywords. That's how people find you from the search engines. Most articles should have a theme. Wedding, sports, gambling, etc. Key in this theme into the tool and make a search. The tool will suggest numerous keywords based on your input. There are a couple of features that I love about this tool.
Firstly, it shows you how many searches are being made for a particular keyword phrase. The greater the number, the more popular a keyword is. Don't be afraid of competition. With a site that is search engine optimized you will still get visitors. I'll elaborate on that later.
The second thing I love about this tool is that it shows the search counts in the most recent month. It's a great tool for measuring CURRENT popularity and you want to write articles that are currently popular to have any kind of chance in the face of fierce competition
Make a list of these keyword phrases. I personally love to have a long list that includes any phrases that have more than 2 words in them. Why? Simply because my traffic reports show that most people arrive at my site by searching for long keyword phrases. That's also how your articles will get traffic and they are very targeted traffic. If you have a product to sell, this kind of traffic would be exactly what you'd be looking for.
Now that you have your list, throw them in the title of your article. Start your article with those keywords as well. There are tons of information out there about keyword density but in my opinion, to follow strictly to keyword density is a little overboard. Time is needed to check your articles on keyword density and as far as I'm concerned, I can make better use of that time. For example, write more articles!
To ensure that your article is optimized, sprinkle your keywords casually in every other paragraph and you should do just fine.
In summary, simple follow the following steps: 1) Research on keywords 2) Make a list of keywords 3) Include these keywords in title 4) Start your article with a popular keyword phrase 5) Sprinkle similar keyword phrases in every other paragraph 6) Write more articles!