Most doctors will send you to a physical therapist who can guide you through this process. Exercises at the beginning of rehab are different from what your knee can handle later. The goal is to get as much motion back as possible without damaging the knee any
further.
The healing graft is under increased strain when the knee is in the fully extended position. Closed kinetic chain exercises with the foot on the floor or other surface strain the ACL less when the hip is bent. An example of this activity would be the mini-squats often prescribed in the early phase of rehab.
High demand exercises such as the lunge can be done when the squat is deemed safe to do after ACL repair. Then comes the step-up, step-down, and sit to stand exercises. These can all done on one leg. Each one puts about the same amount of strain on the healing graft.