What are good exercises do to strengthen previous sports injury (on knee, ankle, calf)?

Here are some. Straight leg raises wall squats single leg squat (only 45 degrees) calf raises and calf drops from a step a formal session with a physical therapist could be worth while to get you on your way previous ankle sprains need specific treatment to improve range and proprioception.
Resistant Band exerc. A resistance band (often also called theraband or rehab band) is a stretchy length of latex which can be used to provide resistance to most exercises. These have proved to be especially popular following injury.

Related Questions

Very bad muscle cramps in upper inside of right leg. No sports injury works out every other day. What could it be.

Myalgia vs. vein. Never ignore exremity pain or cramping. In all probability, this is simply muscle spasm secondary to electrolyte depletion or loss of calcium; nevertheless you must be examined and obtain a venous doppler to rule out a clot ( doubtful, but possible). Read more...