Nancy is a city in northeast of France, préfecture of the département of Meurthe-et-Moselle.
Going West to Paris
There is two options to get to Paris from Nancy. By the highway A31 through Metz and then A4 to Paris, or by the A31 through Toul and then road national 4. For this later option, access to A31 is better by the "Echangeur Ouest" in Laxou. You can walk to a good stop before the highway entrance following the "Paris" road sign present in the city or using the public transportation. http://www.reseau-stan.com (in french) could help locating which bus to take. The destination for the spot is station Vair in Laxou. For Highway through Metz, there is several connection to the A31 from the city center. A good one through Rue de Metz. Walk along this street from city center until you reach a traffic light a little outside of the city. Spots are located on the wiki maps.
Going West to Troyes
If you want to go to the direction of Troyes, somebody told me (and I tried it) to go to the "Croix de Lorraine" building, that is located at the end of the "2" bus line, in the direction of "Sapinière", or, more directly (as said in the "Paris" section), at the "Vair" stop. . I waited plenty of time by a hot and stormy weather, but there is a nice place for cars to stop. Use a sign to go to St-Dizier, as there is not so much people taking the road to Troyes.
Going South towards Épinal
South of Nancy is Jarville-la-Malgrange in which there is an entrance to the highway A330 towards Épinal (the road crosses the eastern side of the urban area of Nancy). You can walk or use buses to go to Avenue Louis Berthou. There, just wait in front of the Automobile Club Lorrain. Lots of cars coming from Nancy use this itinerary to reach the highway. The road is straight and there is plenty of room for cars to park. You should not have too long to wait to get a car. Another road joins up with this one in front of a church a little further ahead but it is harder to get people to stop there.