In my experience the single assignment that causes students in introductory and intermediate level Spanish classes the most worry is the Oral Exam. Often this is the only time these students are graded on their ability to produce Spanish vocally, so it is understandable that they should be somewhat nervous. Here is a list of ideas that will hopefully help students be as prepared as possible, and thus as relaxed as possible, for their oral exams. These ideas are divided into two categories: Preparation for the Oral Exam, and Execution of (during) the Oral Exam. Note that these ideas are mostly specific to the Oral Exam itself. It should go without saying that you need to learn the grammar and vocabulary too if you want to do well!
Preparation: Just like all good evaluations, Oral Exams cannot be satisfactorily done without adequate preparation!
1 - Listen! Research has shown that the best way to improve your ability to speak in a foreign language is to listen to that foreign language. That's probably why your instructor keeps talking to you in Spanish all the time. Not just because they're a jerk, but because they're trying to help you learn more Spanish! Your brain requires a minimum amount of exposure to Spanish that you are paying attention to in order to learn how to process it (and consequently produce it) correctly. So, when your professor talks, listen! Also, it's a good idea to practice outside of the classroom as well. Most textbooks have online listening activities which will bore you to tears, and after you finish with those, watch your favorite movies in the target language! I don't recommend that you watch foreign movies that you're not familiar with. If you watch your favorite movies (e.g. Star Wars) in Spanish, your brain only has to process the Spanish, not the Spanish and the plot.
2 - Practice asking and answering questions! If you've done an Oral Exam before, you already know that the majority of the Oral Exam consists of you and the person(s) you're speaking with asking each other questions. You need to know the question words and how to respond to them! I would suggest that you get together with someone else in the class, and practice asking each other personal questions using the vocabulary form the current and/or previous chapters. (e.g. How many horses do you have?, Do you like pizza?, Where do you live?, What is your credit card number?, etc.)
3 - Practice filler words. This point isn't as important, but it can definitely help. Nothing makes you sound more like a foreigner than using the wrong filler words and sounds (e.g. "um", "so", "like", "well", "eh", etc.) Ask your instructor what the filler words and sounds are for your language and practice using them in class. You'll feel more like a speaker of your target language, and you'll sound more like one too!
4 - Prepare an adaptable/generic intro and a closing. This particular step is especially useful for Oral Exams that are assigned scenarios (e.g. "You meet a stranger in the emergency room, ask each other about your injuries.") You can probably come up with generic openings and closings that can be used in almost any scenario (e.g. "hello, my name is _____. What's your name? It's nice to meet you ____. How are you today? etc.) If you have a good solid opening and closing prepared, you'll be able to start off and finish off strong, which is very important! Those are the places where a lot of the grading can happen! But be ready to adapt them as needed! (i.e. If the scenario involves you talking to a friend, don't ask them what their name is.)
5 - Prepare your body! This final step is often overlooked. You will give your best performance if you are well rested, well hydrated (but not so much that you'll need to go to the restroom), and well nourished (but not stuffed to the point of getting sleepy.) Your brain just works better when it's fueled, lubricated, and rested! It also works better if it's warmed up! The average beginner brain can take from 5 - 10 minutes to switch over to foreign language mode. (Kind of like getting your night vision after walking into the dark from a bright room.) Arrive early to the oral exam with a friend, and start practicing! That way your brain is ready to go when it's time to start the exam.
Execution: All your preparation has brought you to this point, now talk!
1 - Talk! This is an Oral Exam! If you don't talk, there's nothing to grade. If there's nothing to grade, you get a bad grade! If you're in a group, and they're yammering on, interrupt them! You don't want to be rude, but you don't want to fail either. Interrupt like you would in a normal conversation. (e.g. "Say, I like dogs too! Mine is black and his name is Death from Below. etc.) Also, the amount you say can help (as long as it's on track). Part of your grade is often the variety of vocabulary and grammar you use, not just its accuracy, so make sure you talk!
2 - Help partners. In Oral Exams where you are having a conversation with another student, that student can sometimes run into trouble. Maybe they didn't understand your question, maybe they just can't think of anything relevant to say, maybe they're dead. In most cases, one of the best strategies is to give them a little help. After asking a question, if they don't understand you, provide some sample responses (e.g. What's your favorite food? ... My favorite food is spam, what's yours?) If they are giving you answers that are too brief and don't give you enough to work with, ask them follow up questions (e.g. Do you like cats? No. Why not?) But be ready to help them out if they didn't understand your question! Helping a partner out not only helps them get a better grade, it shows that you are able to keep a conversation going, and it gives you more to say, both of which can help your grade!
3 - Remain calm. It will all be over soon. It's not really that big of a deal. Your instructor isn't expecting you to remember or apply everything. So calm down! Signs that you might be overreacting include: talking too fast, giggling, crying, your mind going blank, etc. If you notice any signs that you might be too worried, take a deep breath. And then try to hold as normal a conversation as you can... in the target language, of course. Freaking out will really only have one result, you'll talk less (coherently), and your grade will suffer. So relax. It will all be over soon. And I promise that it will go by much faster than you fear.
4 - Stay on task. It can be a big temptation to try and show off things you have memorized or that you know really well. But if they don't fit with the situation, don't do it! All it will show is that you can't handle the assigned situation, and that's bad. If you're supposed to be talking to a friend about what happened over the holiday, don't start talking about what you're going to do after graduation. The scenarios you are given have been chosen for a reason (usually because they require you to use certain grammar points and vocabulary items), so stick with what you're told to do!
Well, that's all I have for you. In my experience, students who follow these guidelines, and who have been learning the grammar and vocabulary, tend to get the best grades on Oral Exams, so go to it!