This one is a bit tricky, but it's doable (and somewhat broken if you know how to play it right).
As the achievement states, you need to get expert scores on all levels. So the emphasis here is to get the colour combo and chaining done right.
Tip: Know your shortcut keys!
X takes you to the ticket station
Y takes you to the counter
B takes you to the Bus station
Flo will go there automatically and you won't have to maneuver yourself through the tables and get stuck costing you valuable time.
The first level should be straight forward enough, just make sure that the customers are seated on their coloured chair. The higher the multiplier, the better...
This gets trickier as you progress through each level. This is where the podium comes into play.
Here's a technique that is working for me so far, it's not the most elegant, but as long as it does the trick, I'm not going to complain...
First, stand in front of the podium until you have enough customers waiting. As long as you don't move, you should continually fill their heart meters and they won't walk off. Once you have enough customers to fill all the tables, seat them AFTER the podium goes off and refills some of their hearts.
Take their orders as they come in, two at a time if possible. Hit X and repeat until all orders are taken.
Keep an eye out on customers waiting in line. Once they reach about four hearts left, go to the podium (3 might be pushing it, 2 hearts, you're screwed). Customers sitting at the tables are a little more patient than the customers waiting in line it seems.
Once the customers in line are relatively happy again, go to the counter and start serving all the food to all tables, take two, serve two, hit Y. Rinse and repeat until all tables are served. The extra appetizers/bread is optional but they will break your chaining combo and is only worth 100 points, but not giving this to your guests will drop their hearts.
Alternate between giving the bill out to guests who are done and standing by the podium. Once all the guests are gone, then stand by the podium again to boost your guests back to above half their heart meter. Then clean out the tables (pick up two tables, hit B).
When all the tables are cleared, stand by the podium one more time and get their hearts back to full if possible. Then seat the guests to maximize the colour matching for additional points.
Yes, this is a long winded way of getting the achievement, but it's better to do it right the first time than to have to repeat a stage. Don't worry about closing time. Even if the doors are closed, there will still be a steady set of guests who you don't see that are still lined up.
Taking things slowly will guarantee that you'll get enough points to hit expert at all stages even with a few frustrated guests leaving (that will cost you -500 points per table).
Hope this helps, if you need help, just comment and I'll try to answer all questions.