Wallpaper on old wallpaper? Tips and tricks

Thanks for the info. So you recommend only sanding the surface and not using a primer at all? I am not painting the wallpaper, just trying to put wallpaper on top, but yes I'm worried about the oil based paint smell. Although I did rip out the front wall and replaced with plywood sheets and I stained the wood first, thought that smell wouldn't go away, but 1 month later and it doesn't smell like wood stain or paint.