TBH it's just about variation. Sometimes pass it around to get a decent shot off with a big hitter, sometimes play w/ items for time and space to do a megashot, sometimes try to dodge a goal in. What you do depends on the opportunities that arise.
That said though, the cups are tough. But you will get better by playing them. 90% of people playing online are awful atm - they would really benefit from playing in the cups. Crystal is fairly hard but wait till you get to the strikers cup! That is so tough.