To set up furniture items with basic node-based pose spots, first ensure the furniture Root node is centred and rotated perpendicular to the grid, with blue arrow pointing up for floor items, inwards for wall and down for ceiling. And the furniture mesh positioned in relation to it and the items use in IMVU; select each in-turn and zero their "Location" and "Rotation" properties in "Object
In Edit Mode ensure a vertex group named "Root" is assigned; in the 3DView select all ("A"), in "Object Data" Properties "Add" a new group, double-click and rename "Root", uppercase "R", then click "Assign" to apply to the selection.
To include Pose Spots, right-click the large node per group and using the "Translate" and "Rotate" manipulators, position the node relative to the mesh using the (avatar) dummy as a guide. Once the pose spots are in place, briefly hide the dummies, "Object" menu, "Show/Hide", the select all the seat nodes, shift right-click the "Root" node, then from the "Object" menu select "Parent", "Object", "Object (Keep Transform)" ("Object » Parent » Object » Object (Keep Transform)").
For simple pose included furniture this set-up can then be exported to FBX; shift right-click all the objects to be exported, then in "File", select "Export", "FBX" ("File » Export » FBX (.fbx)").
In the Browser that appears, change the file name and save location, then in "Export FBX" options, under "Main" activate "Selected Objects"; under "Armatures" deselect "Add Leaf Bones", leave the remaining settings as is and click "Export FBX" top-right. Blender will parse the scene saving an FBX file ready for import into IMVU.