How do you mentally and physically prepare for BMT when you're not the sporty type?

Start with your feet and your basics, seriously. The thing that wrecked more people than fitness was blisters and not being used to being on your feet all day, so break in a good pair of running shoes now and walk a lot. For pull-ups, if you can't do one yet, do the assisted version and negatives daily, jump up and lower yourself slowly, that builds the exact muscles fast. Also just get used to waking early, the 5.30am wake-ups shock office-brain people more than the physical training does.

Honestly don't over-stress the fitness, BMT is designed for the average and below-average guy, that's the whole point. They start from basics and there's even a longer BMT for those who need more conditioning, so nobody expects you to arrive as an athlete. What you should prepare is your mindset and admin discipline, folding, being punctual, following instructions without kpkb. The guys who suffered were the ones with bad attitude, not weak bodies. Get your body moving a bit now, but mostly prepare to be humble, adaptable and part of a team.

Mentally, the biggest shift is accepting you're no longer an individual, everything is by the section and platoon. As a bookworm used to doing my own thing, the hardest part wasn't the physical stuff, it was learning that if one person is slow everyone gets tekan, so you help the weaker guys and they help you. Build that teamwork mindset now, because lone-wolf attitude gets crushed fast. Physically, just consistently jog and do bodyweight exercises three times a week from today and you'll be middle of the pack by the time you enlist.

I was the exact same, a total sai kang bookworm who couldn't do a single pull-up before enlistment, and I survived BMT fine, so relax a bit. The single best thing you can do now is start running and doing pull-up negatives immediately, even 3 months of prep changes everything, because BMT itself gets you fit through the sheer volume of activity. Focus on the 2.4km run and pull-ups since those are the killers, do the SAF's own strength and conditioning style exercises, jumping jacks, push-ups, and hang from any bar you can find to build grip. What I wish I knew: the mental game matters more than the physical, the non-sporty guys who struggled most were the ones who panicked and gave up, not the weakest ones. If you just keep trying and don't rank last on purpose, the PTIs and your section mates will carry you through, and you'll be shocked how much fitter you are by POP.