1. Get all A's in the pre-reqs.
2. Get observation hours at a variety of places, and make meaningful connections with the PTs you shadow, so that you have great letters of recommendation (and supportive mentors!).
3. Create great relationships with your professors. You will do better in their classes and you will feel comfortable asking for letters. Go to their office hours and chat.
4. When the time comes, put effort into doing well on the GRE.
5. As far as extracurriculars, join an organization that interests you! It doesn't have to be a "pre-PT Club." It's worthwhile to hold a leadership position if you have time.
6. Do some community service. Often times, non-service oriented clubs will have a few volunteer events each year.
7. These days, it's always helpful to have some research experience on your application.
8. Start looking at PT programs now, and pick 2-4 schools that you would really like to attend. Read every single piece of information available about those programs on PTCAS, CAPTE, and this forum. Tailor your application to them.
My #1 super secret piece of advice to succeed in college: Sit in the front row.
While 8 is valuable, I wouldn't worry about it too much right now (as a freshman). Sophmore year and junior give it some more investment, but the programs are likely to change a bit by the time you'd be ready to apply. If you get excited about a program now and find out in three years they're doing a curriculum overhaul.... You see my point I think.
I'd stress the leadership role for 5. It's probably better to be the president/vp/treasurer/whatever of one club than a member in 5. The leadership role shows you actually did something, whereas a member just means you attended some meetings. Also would stress something that interests you. College is a great time to have experiences you'd likely not have elsewhere. Yes, planning ahead is important, but has fencing always interested you? How about boxing? Rock-climbing? Join the club! Or if it's a team that competes with other schools, that's great too! Even if you only practice once a week and maybe go to one tournament a year, you're still part of an athletic team. Not only are you doing something fun, it shows you can work with a group and commit.
Same thing with picking a major. IT DOES NOT MATTER WHAT MAJOR YOU PICK. AT ALL. As long as you complete the pre-reqs, you can get in anywhere with anything. I had a friend with a degree in computer science get into med school. Complete opposite, still works. So pick something you'd like to study throughout your undergrad experience. If that's exercise science, awesome. Wanna study spanish? That's great too (and fairly practical, depending on where you'd like to go to pt school). How about bagpiping? Enjoy! Again, just make sure you make time for your pre-reqs.
Lastly, #3 is pretty key. Take the advice previously given about that. Try to stay in touch with professors you connect well with, as its much smoother asking professor you've been corresponding with monthly/semesterly for a letter of recommendation than one you haven't spoken to since General Biology freshman year.