UPDATE 9/14: A few things have changed for setting up a Twitter application since this tutorial was written. The main change is you will need a phone number to register your app. Most of this guide should be fairly close to the current system, though the screenshots may look a bit different.
Creating Twitter bots, automated text-generators that spew spam, poetry, and other things, can be a bit of a confusing process. This tutorial will hopefully get you through the tough bits and make bot-building possible!
For this tutorial I will be using Python, a language whose simplicity and natural syntax is great for working with text. However, this tutorial should be easily portable to your language of choice. I assume you know at least enough programming to write your own algorithmic text; if you need some help, I would suggest one of the myriad resources including Learn X in Y Minutes. Finally, this post is written from a Mac user’s perspective – if you use another OS and have suggestions or required different steps, my apologies and let me know so I can add them.
If your programming is not up to snuff, you might consider using IFTTT to trigger a Tweet. While the range of possible text is much more limited, you can easily do things like post a Tweet when tomorrow’s weather is forecasted to be nice or you like a video on Vimeo! (You can also use this as a backup for storing your bot’s awesome Tweets.)
You can view the source files used here, screenshots, and other miscellany for this tutorial on GitHub.