I’m trying to edit a body and I need to scale, rotate and move some parts of it to get it to look right. Since I need to do basically the same thing on each side of the body, it would be nice if I could select all the vertices I need on each side and then scale them at the same time, to be sure I do each side by the same amount. The problem I’m having is that scaling this way also moves each side in relation to the other (scale down, they get closer together; scale up, they get further apart) Is there a way to do this without moving them relative to each other?
Is your object symmetrical ?
If so you could split in half and use a mirror modifier
Or use the X-mirror option in the toolshelf and edit one half positioning the pivot point correctly
Or model half the model and use the Mesh / Symmetrize option to copy the changes to the other side of the mesh
Any best method depends on your model and exactly what you want to do. Unfortunately you have omitted this most important info from your post