Since you're asking about the future tense, I'm assuming that you need the verb prácticas in future tense. Here are are the ways its conjugated
Yo practicaré
Tú practicarás
El/ella/usd practicará
Nosotros practicaremos
Vosotros practicaréis
Ellos/ellas/usds practicarán
So it would be
Tú practicarás el piano
I hope this is helpful! The endings come after the -ar, and keep in mind this only works for ar verbs.