It's great that you're concerned about alleviating a potential problem *before* you get pregnant!
Some women with back problems actually find that they have less back pain during pregnancy because the increasingly-large belly counteracts the curve in the spine. Hopefully, you'll be one of those women! If not, there are some back exercises you can do to strengthen the lower back.
For the lower back - stand with feet a little wider than hip distance apart, toes pointing straight ahead, knees bent with hands resting on the tops of the thighs; press your buttocks back, like you're doing a squat, and pull your belly button in toward your backbone to tighten your abdominal muscles; take a deep breath in and as you exhale, lift your torso increasing the arch in your back, tightening the muscles in the lower back; inhale as you return to the starting position; do 8-12 repetitions, rest for 20-30 seconds, and repeat for 2 more sets; be sure to stretch the lower back between sets and when you're completely done by arching your back up like a cat, dropping your chin to your chest and rounding your shoulders while you tuck under your pelvis.
For your upper back - stand with feet a little wider than hip distance, knees slightly bent, abdominals tight; lift your arms straight out in front of you, bend your elbows so they are in line with your shoulders; take a deep breath in, and as you exhale pull your elbows back, squeezing your shoulder blades together by contracting the upper back muscles; inhale as you return to the starting position; do 3 sets of 12-15 repetitions; when you're completely done, stretch the upper back by inhaling as you raise both arms above your head, clasping the hands, and exhaling as you bring the clasped hands down in front of your chest, rounding the upper back and dropping the chin; hold the stretch for a count of 20, breathing while you hold the stretch.
