Question

a good practice for balincing equations with polyatomic ions is what

Answer 1

just search "balancing chemistry equations practice" on google, you'll find a lot of worksheets like this:
http://staff.fcps.net/jswango/unit4/reactions/balancing%20chem%20equations%20WS1.pdf

Answer 2

Treat them the same as elements.

for example to balance the equation:
AlCl3 + Na2SO4 ---> Al2(SO4)3 (ppt) + NaCl

Balance the polyvalent atoms (Al, SO4) first. Then everything else falls into line. You need two Al's on the reactants side, but you also need 3 sulfates, so:

2AlCl3 + 3Na2SO4 ---> Al2(SO4)3 + 6NaCl