Catch rot early
Rot starts where water sits: window sills, the bottom of door frames, trim near the ground, and siding behind downspouts. Small spots can be cut out and patched. Left alone, it spreads into the framing.
Fix the water too
Rot comes back if the water does. After the repair, keep the area painted and caulked. Old caulk around windows is a common cause; see window sealing.
Floors and stairs
A cracked or lifted plank can often be swapped without redoing the floor. Keep leftover planks from the original install. Loose stair treads and wobbly railings are a safety fix worth doing soon.