A rule of thumb for spending effectively is to have a surplus budget as the main objective and thus keep expenses always lower than income. In short, spend less than you earn.
Once you manage to get a surplus budget, that is, spend less than you earn, make it a habit to make savings, both to make dreams come true and to be safe in unforeseen or emergency situations. That is, you must create an emergency fund.
The emergency fund is an amount that should be reserved for eventualities and unforeseen circumstances, understood as the amount needed to help overcome a difficult or unforeseen period.
It is always better to be prepared for the unexpected, than to be caught off guard.