In mock trial, just as in a real courtroom, there are going to be facts that opposing counsel wants out and you want in, and visa versa. That's when objections are made. In order to be effective when objecting and responding to objections, it's important to have good courtroom presentation and the ability to think on your feet. If you're looking for a place to start, then the attached video isn't bad, and it's very important to become familiar with the rules evidence. To help you there, there are flashcards to be found below.