Google Analytics Injector is a plugin which makes it easy for you to start collecting statistic2s with Google Analytics on your WordPress blog.
After the installation of the plugin, click on the "Google Analytics Injector Settings" in the "Settings" menu and add your Google Tracking code (eg. UA-1111111-1) and add you domain.
To be sure the tracking code is not used on the wrong site you could restrict the usage by specifying the site url. This plugin also exclude the visits from the Administrator if he/she is currently logged in.