Spend rings on upgrading your selected character first to increase the duration of the power-ups. Upgrade each of them on your chosen character until they reach the point where the next upgrade costs 9,100 rings. Once there save the gold rings for other uses. Be careful about upgrading every because every upgrade counts towards increasing the Fever meter for everyone. Spend red rings to unlock Amy as soon as possible. She is cheaper than Blaze or Knuckles, and she is the best character. Use her jumping hammer attack to defeat enemies and collect items it hits. She has a wide reach that allows you to score easier, build combos, enter Fever mode, and collect items.