Wrote a long post, so here's a TL;DR: pick whatever major you enjoy, will do well at, and will give you a good backup plan in case dental school doesn't work out. Work hard in school (you should always be busy), don't be lazy, aim to get the highest grade possible, follow all assignment instructions carefully, gain a thorough understanding of the course material in order to get A's on exams (college is a lot harder and more work than high school, trust me), don't get low grades (a few D's or F's will seriously mess with your gpa..even if you repeat them), get a couple hobbies that you enjoy that will help you relax and take a break from studying, meet some cool people who are hard workers and also know how to relax, get the highest science gpa you can possibly get, obtain strong LORs (usually I think it's 2 from science professors, 1 from a dentist you shadowed) by getting high grades and making sure your professor remembers you and your work ethic. The goal is to do the best you can at everything you do, and to always keep improving and doing better than your previous best.
Doesn't matter what your major is.. my advice is pick a major where if you didn't become a dentist that you would have a good backup plan and could do that job for the rest of your life and be happy. For instance, I am a Business Administration major with a concentration in Computer Information Systems and will need to take some extra courses to get the dental school prerequisites compared to a biology major..but I have lots of options with my major if I fail to get into dental school or decide against it (I could do any type of finance/managerial/business job, or I could do any job in computers such as a programmer or systems administrator - and I would be happy in any of these areas, because they are interesting to me and challenging enough).
If you are still undecided on your major, just take GE's and dental prerequisites for now, since you will need both no matter what major you choose.
It's good that you are planning ahead, but don't become too focused on the far future..focus on your current course work. The sooner you are 100% sure what major you want, the better - but it's not the end of the world if you switch your major to one that suits you better. Then you know what courses you need to take to graduate.
All that matters is that you complete the prerequisites (if you are not a biology major then yes you will have to take courses that don't really help you graduate, but are needed for dental school.. don't sweat it though, biology isn't that good of a backup major), get a good gpa, get your shadowing requirements, and get strong LORs.
Take this from a guy who didn't work hard for the last 3 years in college and is just starting to be serious about school: WORK YOUR ASS OFF! Get as high a gpa as you can and have a couple hobbies that you enjoy to take a break from studying - balance is key. Put in 100% effort - this goes for everything in life, not just school. Follow all assignment directions to the letter, study every topic for the quizzes/exams and understand it inside and out. Read all instructions twice or more. Following the instructions is an easy way to get full credit.
I had a 2.5 or so gpa (overall gpa..haven't taken science courses yet..aiming for very high science gpa) when I wasn't taking college seriously. I repeated a couple courses and started getting A's and now I have a 3.26 gpa, and after this quarter I will have 4 more A's so my gpa will be even higher. I am going to work my ass off to raise my gpa as high as possible in school. My goal is to obtain an A in every single class for the rest of my school career - and I know I can do it.. if I get a B a couple times I won't sweat it, but the point is that I'm keeping my goal in mind. I don't doubt that I can achieve a competitive gpa by the time I graduate (I still have 3 more years to go..2 years for my bachelors degree and 1 year for dental prerequisites), and on the bright side I will have an extremely strong upward trend.
That reminds me - repeated courses are included in your gpa calculation on the dental application. So get good grades so that you don't have to repeat any courses, because that D in english that you repeated and got an A in, still includes the D grade on the dental application!
I will warn you right now, to get high grades will take a LOT of hard work and you will be exhausted.. but at the end of the semester when you see those A's on your transcript, it's a damn good feeling and will be well worth all the work you put into it.
