Here is the most common way for wiring a 3 way switch. Bring the power supplyin to one of the switch boxes (one hot, and one neutral), on a #14/2-wire cable. Then, run a #14/3-wire to the other switch location. From the second switch, run a #14/2-wire up to the light box. In the first box, splice the neutral (white) wire from the power supply to the white wire in the 3-wire cable going to the other switch. Attach the hot (black) wire to the common screw on the 3-way switch. The red and the black conductor from the #14/3 cable will be called the ‘travellers’, and will hook up to the two remaining screws on the switch. At the other switch location, you will hook the white wire from the #14/3 to the white wire going up to the light. The ‘travellers’ (black and red) from the #14/3 will connect to the same screws as on the other 3-way switch, and the black wire going to the light will tie on to the ‘common’ screw.