Updating of WordPress post to Twitter has become a nightmare since Twitter requires the user to register an application via api for authentication reason. Though it may sounds daunting for a start especially for less tech savvy users. In fact, update of WordPress post to Twitter can be a breeze with simply just a few clicks using a WordPress plugin.
You will need to register this plugin as an application under Twitter. Just follow the instructions after you have activated the WP to Twitter plugin. The installation will also require you to have an URL shortening account such as bit.ly or etc.