Know What You Need To Know

If you're doing an ad - even a spec ad for your student portfolio - know what you're advertising.
If you're advertising gum, go buy a pack and chew it. Chew it every day for a week.
If you're doing an ad for a car, go to the dealership and sit in it. Take it for a test drive.
If you're doing an ad for insurance, call them up and pretend like you're interested in buying some. You'll get a bunch of junk mail and follow-up phone calls. But you'll probably have a better ad in the end.
A lot of times, students (and even professionals) rely on the internet for research. We watch videos. We read articles. We sit through planners' consumer insights presentations. We think we're too busy for hands-on experience.
We're not.
Get to know your product. Use it. Live with it. See what you love and what you hate about it.
You can do a good ad without ever touching your product.
But without it, it's very difficult to do a great one.