Today's tips is about how you can quickly find keyword with their usage statistics. Simply put, open https://adwords.google.com/select/KeywordToolExternal (will open in a new tab), and type in any generic keyword that is the main topic of your site. For example, you can enter blog or blogging. Then type the confirmation code to make sure you are a human (really!) and hit Get Keyword Ideas. After a while you should be presented with a TON of keywords, each with their statistics.
The columns that you should be paying attentions to includes Advertiser Competition, Approx Avg Search Volume, and Approx Search Volume: (last month). Basically 'Approx Search Volume (last month)' and 'Approx Avg Search Volume' are pointing to the same data: how many times people search for that keyword. Generally, higher values means higher interest to that particular topic.
If you are an AdSense publisher, higher 'Advertiser Competition' means that you won't be running out of ads to display soon. On the other hand, it may also mean more competition for AdWords advertisers, and it might be difficult to get a good traffic, unless you pay more.
This tips is just an introduction to Google Keyword Tool, there's much more to it, depending on how you use the data, so good luck in optimizing it. And it is not the only keyword tool available on the net, so you might as well scour the Web and find other tools.