In order to write a balanced equation, all you have to do is look at your atoms on each side and make sure there are the same amount present on either side.
K 1 | K 1
OH 1 | OH 3
Al 1 | Al 1
NO3 3 | NO3 1
So what you would need to do is add a coefficient in front of each compound to make sure there is the same amounts on either side. Your equation should look like this at the end:
3KOH(aq) + Al(NO3)3(aq) —-> Al(OH)3(s) + 3KNO3(aq)
Make sure that when you are balancing you keep the polyatomic ions together.