As with any speech you must consider your audience - the classroom and the teacher. Put simply, the idea is to speak as you normally would, minus any slang as speeches are supposed to be formal (similar to how when your teacher explains something to you).
Don't use some cool sounding synonyms that nobody but your teacher will understand. Chances are that other students won't know what you're saying, thus reducing the chance that they will be included in the "conversation".
Act as though you are talking to them in first person by using words such as "you", "we" and "our" instead of simply dumping knowledge. The aim of this is to increase engagement, so with all of this in mind practice your speaking skills. Don't be monotone, but also don't try to put on a show and speak in an overly energetic manner (it's incredibly annoying for listeners).