When in town, tap the icon that appear above the cars. Send the cars to the places they need to travel to earn free coins and diamonds. Build decorations in the town to earn coins. Use a combination of fast and slow earning decorations. Although the fast decorations reward you with less coins, you can collect from them often. The slower decorations give you more coins each time they are collected. Save your diamonds until later in the game, when you have more opponents and the tracks have larger rewards.