It is a good idea to change this before you start building content. Its a very easy to do as well. After logging into WordPress as the administrator look under Setting and click on Permalinks. Choose Custom Structure and enter the following code: /%postname%.htm.
Now when you create a new entry and save a draft of it. You will now see the permalink listing directly under the page title. Choose Edit and change the url if needed.
Finally use keywords like my-keyword.htm to reinforce what the page is about.