You can say:
'La cuenta, por favor'
It means literally "The bill, please'.
It sounds ok but if you want to sound a bit more polite you must say:
'Me trae la cuenta por favor?'(Could you bring me the bill please? or 'Traigame la cuenta por favor'(Bring me the bill please).
If you want to use credit card you must ask:
'Puedo pagar con tarjeta de credito?'(Can I pay with credit card?)
When you receive the bill don't forget to say 'Gracias!' (Thanks!)