Voglio is correct but blunt and sounds like a demand at a ticket window. Italian softens it to vorrei, the conditional of volere, followed by a noun or an infinitive. Potrebbe works the same way for asking someone else to do something.
Examples
- Vorrei un biglietto di andata e ritorno per Roma.
- I would like a return ticket to Rome.
- Vorrei viaggiare in prima classe.
- I would like to travel first class.
- Potrebbe dirmi a che ora parte il treno?
- Could you tell me what time the train leaves?
The mistake to avoid
Vorrei is a request; volevo is what you wanted and no longer do.
Where this fits in
Spostarsi, Italian A2: Muoversi in città e in viaggio: trasporti, indicazioni stradali, albergo e biglietti.