I dont find a way to increase cash income in good way. Abnormal player wages, very expensive stadium maintenance. Cash income from all sources are not adequate compared to what expenses are. Winning league, super league or champion league gives you so little cash for example (it's just outdated in this way). Only helps those mysterious balls where you sometimes can get good cash amount or no penalty in maintenance.
If anyone know how to increase cash balance in your way - feel free to share with us.