Ensure that you have a scene with the same number of actors you have available, preferably with men in roles written for men and women in roles written for women. Some roles may be gender neutral, however. Take inventory of the actors' ages, and choose a scene that is age-appropriate. It is best to stay within 10 years above or below your actual age.
You may have been assigned certain requirements for your acting scene. Be sure to stay within these constraints. Common requirements include staying within a certain time limit, picking a scene from a particular genre or era, using text from a particular playwright or performing two contrasting pieces.
Think back to shows that you have seen and enjoyed. It's great to choose a piece that you have some connection to. Search a library's catalogue for books that contain acting scenes, or surf the web for sites that contain texts to browse by searching for something like "acting scenes for two people." Some of these resources will only have the title of the play and the scene that works well for classes or auditions, and then you are required to find the play script. One bit of caution for obtaining works from a database: Read the entire play the scene is from as well. Scene books and websites are starting points; you may act the scene incorrectly if you don't understand the context.
Look for scenes in which you can be doing something other than talking, such as preparing food, cleaning, learning how to dance, observing something or eating. It is much more interesting to watch people than to simply listen to them, and having actions involved gives you a chance to extend your emotions to something other than how you are speaking. Also, if possible, find a climactic scene or one that includes an important event within the context of the play. Make sure the scene you choose has a clear beginning and ending point by choosing one that is within the beats, which are the sub-categories of play scenes. You can know a beat is beginning or ending when there is a change of topic, a change of mood, a new character enters or the location changes.