Something to take into consideration when marking up copy is the degree of creative license you can reasonably take for a given piece without hijacking the script altogether. You may be tempted to make your auditions stand out in a sea of 50+ other auditions, but sometimes standing out is a very bad thing!
When being unique does work, the most memorable commercials get stuck in your head because they feature a voice-over actor with dramatic flair. Brilliant commercials off the top of my head include: Beggin' Strips, Kibbles & Bits, and Meow Mix -- and not just because I'm an animal lover!
Whether the commercial script is animated or not, you will still have to make judgment calls on what "voice" the voice-over job calls for. Answering the basic questions, like whether to use high/low energy or hard/soft sell, etc., are easier to answer than others, like pause here/there or how to make a laundry list sound more distinct. Something to keep in mind: this is not your commercial!
In addition to thinking, "How would I do this commercial if it were my project," consider what the client wants. Ask yourself, "What is the client's goal with this copy?"
Taking the client's objectives into careful consideration will require you to remember everything you learned in voice-over training on breaking down scripts. When you record a commercial script for a client, think of yourself as a consumer and member of the company. How would you want to be sold on the product or service?
Analyzing copy from the client's perspective will also help you become better at selecting voice-over jobs to audition for. Rather than taking the "wet noodle approach" of throwing auditions out there and seeing what sticks, apply for voice-over work that best suits your niche. You will not only save yourself many headaches in the long run, but you will actually become better at 'what you do'.