When you prepare for a voiceover job or audition, it's essential to pay attention to the instruction on the copy. If this is a commercial, the project was likely planned carefully at an advertising agency. Every commercial has a marketing objective. Our job as voice actors is to sell it and make it sound convincing.
Some ad copy will present a problem at the beginning of the script and end with a solution. For example, many PSA's are composed this way. They being with a rather despondent
message, but towards the end, it's all about how they're making progress and how we can help.
There are two ways to prepare for a performance. First, if you're awaiting a live directed session with a client, it's a good idea to read through the script a couple of times just to get the phrasing down but don't practice it profusely. You won't have a clear picture of how the client would like the script performed and reading it over too many times could screw up your performance. So instead, go over it a couple of times to get familiar with the wording but stay directable.
Second, If the client has hired you and just wants you to go off and record on your own, this will call for a different approach. Learn as much as you can from the client. Study the message they are trying to convey in the script and find out as much as you can about the audience they are targeting. This will only help your performance. The more you know, the better you'll perform. If they didn't mention directing you live, suggest it to THEM. It saves a lot of time on revisions. Sometimes clients will be too busy to do it. If that's the case, get them on the phone for ten minutes to discuss the project!
Whether you're performing a script in a directed session or not, there are several important factors to keep in mind to give your best performance. Who are you? Who are you speaking to? Do you think the person you're speaking with believes you? Are you in a park? Are you on a busy city street? Are you talking to college kids? Are you talking to seniors? Are you friendly, sad, excited, goofy, sarcastic or angry?
All of these questions are in play when it comes to delivering a conversational and convincing performance. This goes for any kind of audition opportunity as well. Often, the performance direction is on the script but it's still imperative to ask the above questions to yourself before you record.