Suite101 has a great article on picking effective keywords.
For me, I try to think of things that everyone wants to have or know. For instance, most people want to lose weight, look attractive, make more money and have more free time. These are topics that people will always search for. Creating quality articles that address these topics will help to generate larger audiences.
It's also important to find unique angles within the broader topics. For instance, you might compare and contrast running and walking to see which exercise is best for losing weight.
Once you have your topics, check your keywords on the google adwords site. Type in your keywords to see how many similar keywords have been used in searches recently. You can see how many times each of the keywords has been used. You can also see similar keywords. For instance, i searched jewelry and found that many people searched for that topic spelled like this: jewellery. By including each type of spelling, I could double my views.
Bottom line, keyword research will help you to achieve greater hits on your online articles.