The most confusing convention of staging is the language used to describe how and where actors should move on stage. There are a lot of very technical terms (such as footlights, which are lights at the bottom of the stage) which don't apply to every situation. There are four terms, however, which everyone in the theater will always use when describing movement: upstage, downstage, stage left and stage right. Upstage and downstage refers to moving away from or toward the audience along the depth of the stage. It comes from a time when the stage would be slanted toward the audience, so the place closest to the audience was literally downstage. Stage right and stage left are potentially confusing. They are determined by using the position of the actor when he is facing the audience and they don't change. Stage left and stage right refer to specific zones of the stage rather than a personal "right/left" perspective. So if an actor is facing the back wall of the stage, stage right and stage left don't change despite the fact that the actor's left and right have changed.
Blocking is the movement on stage in a scene. Some blocking is written into the script, but most of it is drafted by the director and refined by the actors. Keep two important things in mind when blocking a scene. First the action should be interesting without being too complex so as to draw attention away from the scene. Second, it is atypical to have actors face away from the audience. It is not entirely unheard of, but it is harder to project towards the "back" of the stage and have the audience hear. It also reduces the emotional effect when the audience cannot see the actor emote.
By far, the most common type of stage is a proscenium stage. Traditionally, this kind of stage has an arch over the front of the stage and an apron which juts out just slightly beyond arch. It has come to mean any stage on which only one side of the stage faces the audience (with or without an arch.) There is also a thrust stage, which looks like a fashion runway to a certain extent. This type of stage has many variations, but it specifically refers to a stage which juts out into the audience. On this type of stage, if an actor faces stage right or stage left, he will have his back to half of the audience. Theater in the round or a back box theater is a third kind of theater in which the stage may be surrounded by the audience so that an actor always has his back to a portion of the audience. The difference between theater in the round and a black box theater is that a black box can be rearranged to fit a more traditional style while a theater in the round cannot.
Theater remains as an art form today because of its ability to grow and change. At one point, it was only performed on a stage, but now theater is performed in all kinds of spaces. From art galleries to the street, theater has broken out of the proscenium arch and into the real world. Even when it is still performed in a theater, pioneers are trying new techniques, such as placing the audience on the back of the stage and having the actors perform in the orchestra pit or even over the seats where the audience normally sits. Because of its versatility, theater is all about experimentation and breaking the rules. The best convention of staging to remember is to follow your instincts -- know when to play by the rules and know when it's time to try something new.