There is no direct preparation required. However, to bring yourself up to speed you may want to practice writing small programs, such as the sample practice problems you can get from your contest point-of-contact contest officials.
During the contest you will not have access to any electronic devices, including calculators. You are allowed to bring with you any amount of written/printed material.
You will also not have access to the Internet during the contest. As such, you may want to bring a reference book for your language. For example, an C++ manual if you are using C++ or a Java book if you are using Java.
For C++ you may also want to bring an STL reference book along with you. If you don't have an STL book, it may help to look into (and print out) some basic functions of <iomanip>, <vector>, <algorithm> and other headers as you see fit. Using STL is not a requirement, but it may help you with development speed during the contest.
Have fun an solve some problems!