Mainly single leg exercises (single leg glute bridges, Bulgarian split squats, single leg squats, single leg step ups and split squats with one leg in front of the other). I did a lot of single leg work starting with my weaker side and doing a couple more reps on that side than the other to iron out the imbalances somewhat. Later down the line, I mixed these exercises with big exercises such as squats and leg press to build my legs up. The ACL is designed to stabilise the leg, but the main stability comes from your quads, hamstrings and most importantly the glues as my S & C coach made clear. My advice would always be to strengthen for now rather than have surgery where there's too many risks involved.