If you have a pull, knock or sprain the first 48hrs are the most important.
If you follow the R.I.C.E. principle you will limit the damage and speed up the recovery.
R - rest - stop using the limb that is damaged (use crutches/sling or just rest) if you don't the damage will get worse.
I - ice - use an ice pack or frozen peas wrapped in a wet towel. This will reduce the pain, swelling and internal bleeding and will speed up recovery time. The larger the muscle the longer the ice needs to be applied to the injury, so about 10/15 minutes every hour for an ankle or 15/20 minutes every hour for a hamstring. Repeat this process for up to 2 days dependent on the severity of the injury. (A word of warning a soak in a hot bath will do the oposite to ice it will increase the swelling and prolong the injury)
C - compression - use a compression bandage or tubigrip bandage, this will also reduce swelling. You must ensure blood flow is not stopped by having the bandage too tight. If the injury is on the leg/arm press the nail and if the colour does not return loosen or remove the bandage.
E - elevation - the injured area should be kept above the heart - so if you have injured your ankle the best place is on the sofa watching the tv with your leg raised up, this will limit the swelling, pain and speed up recovery.