Things I'd have done to set myself up ideally by application time:
1. Look at the different pre-reqs for schools and make sure you take them all so you have a lot of flexibility in terms of where you apply and don't need to worry about taking certain courses at the last minute to be able to matriculate (e.g. anatomy, physiology, biochemistry, microbiology, sufficient English coursework, etc.)
2. Should go without saying but always aim to do as well as possible. Setting good study habits and work ethic early on can make undergrad a breeze. Conversely, a few bad grades can really drag your GPA down and force you into a tough hole you may need to spend years digging yourself out of. Understand that the transition to undergrad from highschool might be challenging but ultimately it is pretty easy to do well in undergrad coursework, and your grade tends to be reflective of how much work you put in. Don't be intimidated and don't be afraid to ask others for help or advice on how to do well.
3. Participate in things that will strengthen your application early on that genuinely interest you. Volunteering, shadowing, research, extracurriculars - these aren't things that should be left for the last minute and done for the sake of having on your resume. Try out different places and experiences until you find the ones you actually enjoy and are passionate about participating in.
4. Always make time for interests outside of anything related to school. Sports, hobbies, exercise, social life, relationships etc. shouldn't need to be sacrificed during your undergrad years unless you're an engineering major/D1 athlete or something really time consuming like that. You don't need to be studying hours and hours every day to do well, and that should leave you with a lot of free time. Don't waste it.
5. Probably a bit too far in advance to be really relevant, but if you set aside even just an hour or two each week to keep your general chemistry/biology/organic chemistry coursework fresh, you could seriously minimize the amount of studying you need to do for the DAT to 1-2 weeks and still do really well.
Enjoy undergrad, with a little bit of time management you can breeze through it without needing to stress.