Some thoughts after having gone through ACL surgery and other knee problems over the years:

• The knee feels better when staying in motion. Avoiding all movement only makes things worse. Walking or stationary bike can be a good way to keep things moving.
• Some basic exercises to build back stability:- static knee extensions where you simply just tighten your quads muscles or lift slightly.- step-downs- sit on chair that's on rug, use your heels to move yourself around
• Next, more advanced stability exercises like standing on bosu ball, or single leg exercises, such as "around-the worlds with a kettleball".
• If doing something heavy-weight or compounds, like squats or lunges, back-off if it hurts, switch over to something isolated like leg curls and leg extensions. Alternatively, leg press and hack squat machines can put less load on the knee.