Here are some short tips and tricks to help you get as far as possible in the game.
Doughnuts are a useful and pretty much essential part of the game. Doughnuts regenerate at a rate of 1 every 5 minutes. But if you need more quickly you can use UPGRADE MAX DONUTS BAR to increase your total doughnut limit and fill the up the doughnut bar for often quite cheaper that in the store during lower levels.
If you are about to level up and have a full or nearly full doughnut bar then make sure you spend most or all of your doughnuts so then you can refill your doughnut bar again, you will have used this to your advantage and you will get to spend as many doughnuts as possible.
In your collection when viewing a new car remember to take the doughnut especially when viewing multiple cars as closing a car stats. window and opening another one will cause you to lose the free doughnut if not taken.
Get the most from sales if you are going to stop playing for a while, for example a meeting or before you go to sleep. You could set the price according to the est. wait time. To get more money you can also buy all of the add-ons to increase the selling price you can get for the time you want to sell for.
In racing change gears when the needle hits the red line/section so that you can get the most speed before changing gears. This is a 'make or break' point at the first gear change (1>2) where even a millisecond can leave you at a disadvantage.