There is the wall join tool, which you just place over the intersection, then click next, miter, etc until you get the join you want.
As for tips
1. pull away interior walls, get the exterior condition the way you want, then extend the interior wall back to the exterior wall.
2. Make sure your wall structure, substrate, and finish layers are set appropriately, ie, structure within the core boundary, finishes outside it. Note the like function layers will join with eachother, so core elements will extend into meet eachother and finishe will wrap together if properly assigned.
3. Try to make walls that join have the same ht constraints. You run inot problems with stacked walls because revit has to figure out too many options.