Hi! Wherever your power is coming in, say one of the 3-way switch boxes, then one would do 2 things:
1) Wire the hot on the incoming to the common on the 3-way, and also wire a 2 conductor w/ground from the incoming power (hot and neutral) that will go to your receptacle. (Black, White and ground)
2) Take the 3 conductor with ground and land the black and red on the remaining 2 terminals of the 3-way switch and then at the other 3-way land the black and red to those terminals. Also in the first switch box, wire the common (neutral; white) to the white on the 3 conductor as well as the ground on the 3 conductor to the ground on the incoming.
Lastly wire the 2nd 3-way to the light wire, landing the black wire from the light on common of the 2nd 3-way and splicing the neutrals together (the one from the light and the one from the 3-conductor) Make sure everything is grounded, including boxes.
Hopefully this helped and you may already know this.