Well basically this is one of the best hints youll probably able to find unless you have discovered it for yourself. Firstly you have to have reached the level where you get the podium.
Then first thing you should do once the level starts, it to go to the podium and start talking to the customers. Keep doing this until you have got enough people per all tables. E.g. If you have 2 tables of two and one of 4.
Wait until you have 2 groups of 2 and one group of 4 then seat them at the same time. Wait for the orders and take 2 of them at a time then the final. Then when the meals are ready take them out. The more you do at once the bigger the chain bonus.
E.g. Take all 3 meals at the same time. When you have all the meals on the tables start talking to customers at the podium. Then once the heart has completely filled the customers will have finished eating.
Clear all the tables before seating anymore customers. Repeat the process and youll be complete the levels and get expert scores a lot quicker.