The key to hitting the expert scores are combos. Combos are achieved by repeating actions, for example: If you take an order then immediately take someone else's order you will receive a 2X combo. Now if you take a third order immediately after that, you will receive a 3X combo. Anytime you interrupt an action by doing something else, your combo will be broken. You will also gain extra points by seating people in the seat that matches the colour of their outfit. On a side note you can hit to rotate the patrons while you are seating them so that you can match them up with the proper colour seat in the booth.
What I would do is start out by seating everyone first, if possible try to fill all the seats, because this will increase the maximum combo possible. Now take everybody's order and after everyone's order is taken, serve the food to everybody and once they have all eaten give them all their bills. Finally, once they have, left clean all the tables. On the later levels you must be quick but you will receive a podium, which I personally thought made the game easier. When you stand next to the podium for a few seconds you will grant everyone waiting in line 3 extra hearts. Here's how I did it: I seated everyone and as they looked over the menu I stood next to the podium until everyone in line received their hearts, then go back and take everybody's order and serve their food. After serving everyone I stood next to the podium again, then handed out bills, followed by cleaning the tables. This ensured I could keep working on my combos with the seated guests without losing anyone who stood in line too long. Losing customers is by far the most harmful thing you can do so always watch their hearts and adjust as necessary to avoid losing hearts. Once a patron loses all of their hearts they will leave thus resulting in negative score. Remember, standing at the podium does not count as an action, thus it will not break your combos, so use it whenever you see fit.
As you progress to the third and fourth restaurant you will have to start serving out all you can eat items. I didn’t worry about these requests too much if its was going to break my combos or bring me away from the podium. With these tips in mind you shouldn't have too much trouble, for the most part I was able to obtain the expert score on my first try and if I didn't, I quit the game and replayed the level. The levels seem to be set up pretty similar if not exactly the same when you replay them.
Thanks to lade73 for showing me the way of the combos.