If two sets enter the box - If conductors are tapped together in the box, remove the wire nuts and connect a piece of wire about 7" long to the black and white groups and replace the wire nuts. Look at your receptacle and you should see a thin flat copper strip with a small bent tab sticking up between the screw on each side of the receptacle. Take a pair of pliers and break the strip and remove the piece completely that breaks free. You then attach the two 7" leads under one screw on each side of the receptacle and attach the two wires from the switch to the other two. This is called split wiring a receptacle.
If power enters the switch box first you will need a length of 4-wire conductor (red, black, white, ground) to replace the wire from the switch to the receptacle box. The rest is about the same in regards to breaking the copper strip, but you will need two 7" pieces of white insulated wire to tap together and connect to the screws on the same side of the receptacle. The red connects under one screw on the other side and the black under the other.