The way to get the attention of the waiter in Spain or Latin America may not sound very polite but it is the common to say it:

Spain: Camarero! (Waiter!)
Argentina: Mozo! (Waiter!)
Mesero! (Latin America!)

If you are not happy with this and want to sound more polite you can add 'please', it would be like this:

Camarero (Mozo/Mesero) por favor!

The following is a list of useful phrases you may use at a restaurant when taking to your waiter:

-La cuenta por favor (the check please)
-He terminado (I'm finished)
-Puede llevarse los platos por favor (please clear the plates)
-Estaba buenisimo / muy rico / delicioso (It was very good / delicious)