You should be quite good at circling by now, and should have learned the sounds as well. You should now start learning when and when not to use your bombs. It can be very tempting to use them when things get tough but try to make sure you have no choice first. The other side to this is to make sure you don't get to risky. Using your bombs wont get you any points but it will keep you alive, which in return helps you build your multiplier. The multiplier is going to be your best friend because around this time your points are going to start flying by.