There are numerous books and guides to help you prepare for your next coding job interview, one element of which will mostly likely be an actual programming test. Certainly, you should known before you get to your interview which programming language you are going to offer up. “I've seen many candidates go into an interview and decide on the spot they wanted to use Scala instead of Ruby. Or C instead of Java. Mistake. Pick one language and stick with it for all your time studying & interviewing,” says Phillip Youssef on his blog. He has several other study tips as well, such as “Many candidates get dinged for jumping into a question they don't really understand.”
Dice also has some great suggestions on this topic, including making sure you show your work and show how you think about a particular problem, make sure your handwriting is legible (many coding tests just use pencil and paper old school), and take notes after the interview about what you think you did right and wrong, so you can improve for the next one.