You do not have to serve customers exactly what they want, especially when playing the free version and cannot prepare their request. Bake your best donut and give it to them to still get some money in return.
Head to head contests
Winning head to head contests can be difficult. Rolled donuts usually perform best, especially when mixed and matched perfectly for a great and colorful presentation. Watch the votes you can cast to see which are winning and remember how the donuts are made. Then, reproduce those designs. Add complementary colors, items that the other participants do not have, and keep trying.
Ingredients
Watch advertising videos to unlock new ingredients for free. They will provide an advantage, especially in the daily contests where you will now have more choices.
Production
Wait for the customers to arrive before baking donuts at the start of every day. They will not leave, and you will know exactly what to make to get the biggest profit after they are served.