My advice is to practise.
In British English some nouns end in -ice and the corresponding verbs in -ise:
licence/license (without the i)
In American English noun and verb have the same form; the s is retained in license/license, and the c in practice/practice.
Some words take the same form as verb and noun:
Disguise, exercise, franchise, invoice, merchandise, notice, promise, sacrifice, slice, surprise
Service is a noun but it is also used as a verb: I need to service my car. However, the word has taken on a sexual connotation and you should avoid using it as a verb with one or more persons as direct object. Use serve, help, aid or assist instead.