Well first off you've come to the right place.
What year are you? If you're a first year just getting used to college, you have time to bring you're GPA up. There are a lot of factor which can make you look more attractive to schools, just knowing how can make all the difference. I'll give you a breakdown of what i think is important. You can always PM me and we can discuss it in more detail.
First off, getting exposure in any field shows you have taken the time to make sure this is what you want to do. A lot of people think medicine/dentistry is for them cos they hear about the magical salaries and incomes some doc have. If this happens to be you, honestly Investment banking is MUCH more lucrative (another thing i can tell all about). Shadowing is very important cos dental school is a huge investment of your time, energy and money.
Volunteering in the medical arena and in the dental arena shows you considered both. This is what i did. I strongly recommend not limiting yourself. When i interviewed all the schools noticed I volunteered in the hospital in the ER and PICU. They asked about it, and i told them that i wanted as much exposure to medicine as i could get. On top of that I told them I shadowed an anesthiologist, OB/GYN, Neurosurgeon and an Oral Surgeon. For me, I knew i waned to be a practicioner of dental Medicine, but had to make sure while i had the time. So in essense volunteering and shadowing make you look mature. Because you learned about the profession (while helping).
Hope this helps, like i said if you wanna ask me personal PM me and i'll give you the low-down.
All the best.