Look to do all of the upgades for that level, do the medical center and the pitch first then the acadamy as these all help reduce injuries(supposedly)! After that work your way along. Some players like to upgrade the groung a lot thinking that they will get lots of money but I think you then tend to set the ticket price to high and struggle to get a full attendance so l believe in gradual exspantion piece by piece, once I've done all of them I start over.