You should apply ice to the knee 3 to 4 times per day.
Use a short knee brace to temporarily immobilize the knee and give rest to the ligaments in and around the knee.
Avoid any high flexion activities.
Next Steps
If the pain persists beyond three days, it would be a good idea to consult a knee specialist, who will first do a thorough examination and possibly X-ray of the knee. Most ligament injuries resolve well with anti-inflammatory medicines and physiotherapy.
Health Tips
Anytime the pain and/or swelling increases out of proportion to what it was before, you should immediately consult a knee sports specialist.